



*These authors contributed equally to this work










Materials and Methods

Ethics Statement


Study Species and husbandry



Parameter n inital Initial period n exposure Exposure period
C aquarium T aquarium C aquarium T aquarium

Nutrient Enrichment


Short-term Calcification Measurements Before and After Nutrient Enrichment







Determination of Zooxanthellae Density


Statistical Analysis




Effects of Nutrient Enrichment on Zooxanthellae Density







Effects of DIC on Calcification at Baseline and Increased Zooxanthellae Densities






Factor F df p
Nutrient enrichment 11.697 1 0.042*
DIC 249.560 1 0.001*
Nutrient enrichment*DIC 4.253 1 0.131
*Indicates a significant effect (p<0.05).













The effect of pH, alkalinity, and calcium on hermatypic corals Are reefkeepers striving for the right levels of pH, alkalinity, and calcium? Using PAM fluorometry, Christie D. Raji studies the effects of high and low levels of each of these parameters on hermatypic corals in a captive environment. Click through to see the images.



Coral reefs are rapidly disappearing as carbon dioxide emissions, cyanide fishing, and eutrophication increase. Antithetically, the reef aquarium trade has experienced an increase of demand, although many aquarists have an absent understanding of seawater chemistry and coral physiology. In this study, the health of three hermatypic coral species (Caulastrea furcata, Pavona decussata, and Pocillopora damicornis) were analyzed via PAM fluorometry in hostile water conditions. The calcium, alkalinity, and pH parameters were altered to match ocean acidification conditions and extreme low and high values that are reached due to improper dosing in an aquarium. Among the species examined, the maximum potential quantum yield (Fv/Fm) was significantly affected in hostile conditions. Specifically, a decline in health was observed in elevated alkalinity and in decreased calcium conditions. Furthermore, corals did not exhibit a negative response in Fv/Fm during low pH conditions.



Hermatypic (reef building) corals are rapidly disappearing due to dredging, cyanide fishing, eutrophication, overharvesting, and increasing sea surface temperatures (Edinger et al. 1998, Hughes et al. 2003, Marubini and Thake 1999). However, to fully understand the direct biochemical effect on corals, the anatomy and physiology of these corals must also be understood.

All hermatypic corals are made of an aragonite skeleton which is a crystalized form of calcium carbonate (CaCO3) (Barnes 1970). With the continuous increase of carbon dioxide into the atmosphere, the ocean has experienced an increase of carbonic acid. Carbonic acid inhibits the exchange of hydrogen ions which eliminates the production of calcium carbonate and decreases pH (Marubini and Atkinson 1999). Without the production of calcium carbonate, coral skeletons weaken and in time degrade completely (Kleypas and Langdon 2000). This process is has been linked to the lack of recovery in coral reefs that have been exposed to dynamite and cyanide fishing practices (Hilbertz 1981 and Jones et al. 1999).

Zooxanthellae (Frudenthal, 1962) have a mutualistic symbiotic relationship with their hermatypic hosts; in return for habitat and nutrients, the zooxanthellae provide photochemically useable energy for the coral, thus accounting for a large portion of a coral's net energy (Knowlton and Rohwer 2003 and Muscatine and Porter 1977). When water quality reaches unsuitable levels or temperatures become too high, the coral host discontinues the relationship by abandoning, or releasing, the zooxanthellae from its tissues (commonly known as "bleaching"). Coral bleaching has intensified throughout the years and has been the leading cause for the deaths of reefs; including the largest reef in the world, the Great Barrier Reef (Brown 1997 and McCowan et al. 2012). Bleaching has also been observed in aquaria much like a natural reef when water quality is poor or if the temperature is allowed to become suboptimal (Donowitz 2002).

The biodiversity of coral reef habitats has driven an increased interest in tropical reef aquaria across the world (Jones et al. 1999). With advancing husbandry technology (e.g. wave makers, light structures, and mechanical filtration systems), reef aquaria have become easier to own and maintain. With this advancement of mechanical components, there has also been the advancement of water treatment. Aquarium supply companies, such as Seachem and Kent Marine, are bettering chemical treatment for optimal water quality specifically for coral health. The most common water quality parameters tested for and treated within a reef aquarium are alkalinity, calcium, and pH (Donowitz 2002). In order for corals to thrive, these parameters must be maintained at certain levels to create a balanced seawater solution. Natural seawater typically hasan alkalinity of 2.5 meq/L, a pH of 8.2, and a calcium of 410 ppm (Holmes-Farley 2005). In reef aquaria, these parameters are kept at higher levels; alkalinity=3.0-3.5 meq/L, pH=8.2-8.4, and calcium=420-450 ppm. The upkeep of these parameters is maintained via "dosing", and are often divided into two parts: 1) a calcium chloride solution with added trace elements and 2) a bicarbonate and carbonate solution (alkalinity). When dosed improperly, these parameters can cause an increase of supersaturation, increasing the likelihood of CaCO3 precipitation; also known as "crashing the system" (Holmes-Farley 2005). The precipitation of CaCO3 can be detrimental to corals in a closed system such as a reef aquarium.

When evaluating coral health, the few methods that are currently available are expensive and can come with high error. Littman et al. (2008) compares the accuracy of a hemocytometer to a flow cytometer; measuring the densities of free living zooxanthellae. Many are beginning to adopt this hemocytometer method, which consists of scraping the tissue off of a coral, preserving it in a formalin solution, and then counting the zooxanthellae cells that detached from the tissue (Suwa et al. 2008).

However, a newer and less invasive method called PAM chlorophyll fluorometry has been favored and used since the early 1990's (Jones et al 1999, Suwa et al. 2008, and Kramer et al. 2012). This method provides a measurement of maximum potential quantum yield (Fv/Fm), which is the variance of minimum and maximum fluorescence divided by the maximum fluorescence. In short, the fluorometer measures how efficiently the zooxanthellae convert light into photochemically usable energy for the coral (Jones et al 1999, Suwa et al. 2008, Kramer et al. 2012, McCowen et al. 2012, and Zartler 2012). This method can be applied in a home aquarium using the smaller and less expensive Heinz Walz Jr. PAM chlorophyll fluorometer (Zartler 2012).

Within this experiment I analyzed the health of three hermatypic coral species (Pavona decussata, Pocillopora damicornis, and Caulastrea furcata) was analyzed via PAM fluorometry in hostile water conditions. Calcium, alkalinity, and pH were altered to match (1) scenarios in relation to ocean acidification and (2) extremely low and high potential values reached in an aquarium due to improper dosing. The purpose of this study is to understand the direct effects of poor (or hostile) water quality has on hermatypic corals in a captive environment and to better understand the potential impacts of ocean acidification on these corals.


Experimental Design

Seven 5-gallon aquariums were positioned 7 cm apart on a cabinet top in the Biology Lab at Alaska Pacific University (APU). Each aquarium was labeled in accordance to a specific experimental treatment (Table 1). A plastic container was placed in each tank and filled with live sand and amphipods that were previously cultured in a well-established aquarium for biological filtration. The live sand was oxygenated with an air pump to support proper circulation. Additionally, hang-on-back filters were set up on each system containing a filter sponge and activated carbon for mechanical and chemical filtration. Water quality was maintained at natural seawater conditions by applying weekly partial water changes (10 %) using Red Sea Salt mix, until treatments began.

Collection of Specimens

Fragments of the three hermatypic coral species, C. furcata, P. decussata, and P. damicornis, were clipped with bone cutters from their parent colonies that have been long established in a display tank in APU's Aquarium Lab. Twenty-one fragments of each species were prepared (average length of 5 cm). Individual fragments were cut specifically by species: 2-3 polyps for each C. furcata, 1-2 "chips" for each P. decussata, and 2-3 branches for each P. damicornis (Figure 1). Once the corals were fragmented, each set of polyps, chips, and branches was placed on a 3 cm long ceramic plug and attached using cyanoacrylate adhesive. The fragged corals were then uniformly distributed and acclimated into seven different experimental tanks (three frags of each species per tank). All tanks were cultured 2 months prior to the time of acclimation.


Figure 1. Coral fragments of the three species C. furcata (left), P. decussata (middle), and P. damicornis (right).

Water Quality Manipulation

A 33% solution of Hydrochloric acid (HClaq) was used to reduce and maintain a low pH of 7.9 in the "Low pH" system. This was achieved by dosing 0.25 mL of HClaq every 10 minutes for ~2-3 hours, 3 times a week for one week prior to the fluorometry sampling dates. The "High pH" system was dosed with a 42 % solution of Limewater and maintained a high pH of 8.35-8.40. The dosing procedures were the same as those of the low pH.

The "Low Alkalinity" system was kept at 1.5 meq/L by dosing 0.625 grams of Seachem's Reef Builder calcium additive 4 times every 10 minutes, 1-3 times a week, given the previous week's water quality results. A calcium additive, Seachem's Reef Carbonate, was used to decrease alkalinity because of the negative relationship of the two parameters in a reef aquarium (Seachem Laboratories Inc 2004. In order to achieve and maintain a high alkalinity of 7.0 meq/L, 0.6 grams of Seachem's Reef Carbonate alkalinity additive was dosed 4 times to the "High Alkalinity" system every 10 minutes, 3 times a week.

The "Low Calcium" system was maintained at 350 ppm by dosing 0.6 grams of Seachem's Reef Carbonate additive 4 times, every 10 minutes 1-3 times a week (based on the previous week's water quality results). The "High Calcium" system was maintained between 500- 600 ppm, by dosing 0.625 grams of Seachem's Reef Builder calcium additive, 4 times every 10 minutes, 3 times a week.

Water Quality Analysis

Water quality was tested using Seachem's Marine Basic test kit (Seachem Laboratories Inc., 2004), which measures the following parameters: pH, alkalinity (meq/L), nitrite and nitrate (mg/L), total (or ionized) and free ammonia (mg/L). Every parameter previously listed was assessed. Nitrate and nitrite generally peak when excess nutrients are added to a system which could cause stress among corals. It was important to maintain these at 0.00 mg/L during the entire duration of this experiment (Hughes et al. 2003). Additionally, ammonia is toxic in an aquarium and should also be kept at 0.00 mg/L (Seachem Laboratories Inc. 2004). Temperature was maintained at 26°C for all tanks. Salinities were also measured daily using an optical refractometer and all systems were maintained at a range of 33-34 ppt for the duration of the experiment.

Fluorometry Sampling

Fluorometry sampling followed the methods of Kramer et al. (2013). A Heinz Walz Jr-PAM (Pulse Amplitude Modulated) chlorophyll fluorometer with a 450 nm pulse applied through a 100 cm and 1.5 mm diameter fiber optic cable was used to derive maximum potential quantum yield. Measurements were taken less than 1mm from and parallel to the corals' coenosarc (polyp- connecting tissue). PAM WinControl-3 software was used when applying saturating pulses.

Statistical Analysis

Multiple regression was used to determine the response of maximum potential quantum yield in relation to the changes of pH, alkalinity, and calcium with a species effect. Due to unexplained deaths, nine P. damicornis fragments were not considered in this analysis. All data was analyzed in the software program "R" (R Core Team 2012).




There was a significant difference in the maximum potential quantum yield among species by pH (F = (3, 328) 15.1, p-value < 0.001), see Figure 2a; however, there was a weak relationship (r2 = 0.121), see Figure 3b. C. furcata and P. damicornis had a significant difference (p-value < 0.05), and P. decussata, showed no significant difference (p-value = 0.143). Among all species there was a noticeable peak in Fv/Fm around 8.2.


The maximum potential quantum yield showed species-specific responses to changes in the alkalinity (F = (3, 328) 43.1, p-value < 0.001), see Figure 2b. Similar to pH, a weak relationship (r2 = 0.283) was observed (Figure 3a). Additionally, C. furcata and P.damicornis both had a significant difference (p-values < 0.001) in Fv/Fm, however P. decussata did not (p-value = 0.107).


There was a significant difference in maximum potential quantum yield values among the calcium treatments of the three species (F = (3, 319) 17.0, p-value < 0.001), see Figure 2c. However, similar to pH and alkalinity there was a weak relationship (r2 = 0.134), see Figure 3c. Specifically there was a significant effect among C. furcata and P. damicornis (p-values < 0.001). Again, P. decussata was not significantly affected (p-value = 0.124). A noticeable minimum threshold of approximately 375 ppm was observed among all species.


Figure 2. A general overview of the changes of the maximum potential quantum yield by each parameter scenario (high and low) compared to the reference. Sea green represents C. furcata, green represents P. decussata, and brown represents P. damicornis. Each bar is within 2 standard errors of the mean.


Among these species examined, corals experienced health effects when exposed to hostile levels of pH, alkalinity, and calcium. However, it is important to note that P. decussata experienced no significant changes in any parameter, indicating that coral species have different responses in hostile environments. For instance P. decussata experienced a slightly higher Fv/Fm within the high calcium treatment compared to C. furcata and P. damicornis. All species reacted negatively to low calcium concentrations (300-350 ppm) with an apparent minimum threshold around 375 ppm. This threshold should be considered when maintaining aquacultures.

Aquarist most often maintain elevated levels of pH, alkalinity, and calcium to promote coral health. In this study however, elevated conditions of these parameters resulted in a decline of photosynthetic efficiency (Fv/Fm), indicating an overall decrease in coral health. There was also a slight decrease in health as parameter values increased within the recommended ranges. This effect should be considered when dosing in a closed system as corals experienced optimal health within the lower values of the recommended ranges.


Figure 3. The changes of the maximum potential quantum yield with the changes of pH, alkalinity, and calcium by species. The shaded boxes represent the ranges for recommended for coral. The positive relationship of alkalinity and pH and the negative relationship of alkalinity and calcium should be considered when interpreting results.

Ocean Acidification

While there were no significant changes observed in coral health between pH treatments, it is important to note that hydrochloric acid was used in place of carbon dioxide. While pH was altered, there was no net increase of carbonic acid, as projections indicate as a result of carbon dioxide sequestration. A decrease in pH is known to decrease the net calcification of hermatypic corals due to the reduction of alkalinity; however, photochemical efficiency showed no significant change during this study. This is important in that projected pH levels (i.e. 7.9) do not appear to significantly affect the photochemistry of zooxanthellae. This indicates the need for better understanding of the relationship between zooxanthellae and their coral host to accurately predict the changes in population dynamics that may result from ocean acidification.

Coral Aquaculture

As shown by Zartler (2012), individual coral species respond differently to changes in temperature within the recommended range for aquaculture. Similarly, this study shows that individual species respond differently to pH, alkalinity, and calcium. For instance, P. decussata and C. furcata are highly adaptive corals that have a small negative response in hostile water quality environments, and can be considered as ideal beginner corals. Whereas, P. damicornis has a smaller range of tolerance and would be more affected in the event of overdosing. This information can be used when determining the skill level required of an aquarist to maintain a specific species (easy/moderate/difficult), and should be considered when devising dosing procedures for aquaculture.

Table 1. Experimental tanks and their parameter scenarios. The parameter goal was the predicted value and the parameter mean is the average of the actual values. The additive represents the additive that was used to achieve the parameter mean. Tank 7 was a reference tank at optimal (natural) water quality which was achieved by partial water changes without additives.
Tank Parameter Parameter Goal Parameter Mean Additive
1 High pH 8.7 8.28 Limewater
2 Low pH 7.7 8.07 Hydrochloric acid
3 High Alkalinity 5.0-8.0 meq/L 4.9 meq/L Seachem's Alkalinity
4 Low Alkalinity ~1.0 meq/L 2.0 meq/L Seachem's Alkalinity
5 High Calcium 500-800ppm 530ppm Seachem's Calcium
6 Low Calcium 250-300ppm 386ppm Seachem's Calcium
7 Reference Optimal - None


Literature Cited

  1. Barnes, D. (1970). Coral Skeletons: An Explanation of Their Growth and Structure. Science. 170: 1305-1308.
  2. Brown, B. (1997).Coral Bleaching: causes and consequences. Coral Reefs. 16, S129-S138.
  3. Donowitz, R. (2002). Reefkeeping 102: Terms and Concepts to be Grasped. Advanced Aquarist. 1.
  4. Edinger, E., Jompa, J., Limmon, G.V., Widjatmoko, W., and Risk, M.J. (1998). Reef Degradation and Coral Biodiversity in Indonesia: Effects of Land-based Pollution, Destructive Fishing Practices, and Changes Over Time. Marine Pollution Bulletin. 36: 617-630.
  5. Freudenthal, H.D. (1962). Symbiodinium gen. nov. and Symbiodinium microadriaticum sp. nov., a zooxanthellae: taxonomy, life cycle, and morphology. Eukaryot Microbiology. 9:45-52.
  6. Heinz Walz GmbH. (2007). Junior-PAM chlorophyll fluorometer operator's guide. 6: 43-46.
  7. Hilbertz, W. (1981) Mineral Accretion of Large Surface Structures, Building Components and Elements. United States Patent. 4,246,075.
  8. Holmes-Farley, R. (2005). What is that Precipitate in My Reef Aquarium?. Reef Central Magazine.
  9. Hughes, T.P., Baird, A.H., Bellwood, D.R., Card, M., Conolly, S.R., Folke, C., Grosberg, R., Jones, Hoegh-Guldberg, O., Jackson, J.B.C., Kleypas, J., Lough, J.M., Marshall, P., Nystrom, M., Palumbi, S.R., Pandolfi, J.M., Rosen, B., and Roughgarden, J. (2003). Climate change, human impacts, and the resilience of coral reefs. Science. 301: 929-933.
  10. Jones, R.J., Kildea, T., and Hoegh-Guldberg, O. (1999). PAM Chlorophyll Fluorometry: a new in situ technique for stress assessment in scleractinian corals, used to examine the effects of cyanide from cyanide fishing. Marine Pollution Bulletin. 38, 864-874.
  11. Kleypas, J. and Langdon, C. (2000). Overview of carbon dioxide induced changes in seawater chemistry. 9th International Coral Reef Symposium. 2: 1085-1090.
  12. Knowlton, N. and Rohwer, F. (2003). Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat. The American Naturalist. 162.
  13. Kramer, W.E., Schrameyer, V., Hill, R., Ralph, P.J., and Bischof, K. (2013). PSII activity and pigment dynamics of Symbiodinium in two Indo-Pacific corals exposed to short-term high-light stress. Marine Biology. 160: 563-577
  14. Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., Goddard, J., Marubini, F., Aceves, H., Barnett, H., and Atkinson, M.J. (2000). Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef. Global Biogeochemical Cycles. 14, 639-654.
  15. Littman, R.A., van Oppen, J.H.M., and Willis, B.L. (2008). Methods for sampling free-living Symbiodinium (zooxanthellae) and their distribution and abundance at Lizard Island (Great Barrier Reef). Journal of Experimental Marine Biology and Ecology. 364: 48-53.
  16. Marubini, F. and Atkinson, M.J. (1999). Effects of lowered pH and elevated nitrate on coral calcification. Marine Ecology Progress Series. 188: 117-121.
  17. Marubini, F. and Thake, B. (1999). Bicarbonate addition promotes coral growth. Limnology and Oceanography. 44: 716-720.
  18. McCowan, D.M., Pratchett, M.S., and Baird, A.H. (2012). Bleaching susceptibility and mortality among corals with differing growth forms. 12th International Coral Reef Symposium. 9A.
  19. Muscatine, L. and Porter, J. (1977). Reef corals: mutualistic symbioses adapted to nutrient-poor environments. Bioscience. 27:454-460.
  20. Seachem Laboratories Incorporated. (2004). Marine Basic Test Kit Manual.
  21. Suwa, R., Hirose, M., and Hidaka, M. (2008). Seasonal fluctuation in zooxanthellar genotype composition and photophysiology in the corals Pavona divaricate and P.decussata. Marine Ecology Progress Series. 361: 129-137.
  22. Zartler, Z.K. (2012). Applying PAM fluorometry for the advancement of coral aquaculture. Advanced Aquarist.11: 28-34.

No publisher Christie D. Rajcic, B.S. Pomacanthus Publications, Inc. Alkalinity B.S. Aquarium Corals Calcium Christie D. Raji pH 2014-07-30T13:00:00Z Page
Aquarium Fish: Chloroquine: A "New" Drug for Treating Fish Diseases While not a panacea or miracle drug, chloroquine is experiencing resurgence in popularity for use in fish-only aquariums and quarantine systems to treat a variety of problems ranging from Cryptocaryon to Aiptasia anemone infestations. Click through to see the images.


In early the 1970's, when I was just 13 or so, Cryptocaryon irritans ("marine ich") and Amyloodinium ocellatum ("marine velvet") were a bit less of a problem for my fish than they are now when I quarantine new fish as an aquarium curator. The reason was a product called Marex from the Aquatronics Corporation (they have long ceased operations). Marex was sort of a wonder drug for us back then - simply adding a single $1.99 dose protected the fish in a 50 gallon aquarium from many diseases plus it killed the unsightly algae that grew all over the tank decorations back in those days! When the company went out of business I moved on to using other products. For the past 25 years, I've been using ionic copper measured with a spectrophotometer twice a day to control marine ich and other protozoan diseases. Copper is slow to affect a cure, and the difference between a therapeutic dose and a dose harmful to some fish species is slight. Still, it seemed to be the best method for quarantining or treating active diseases in fish. Thinking back to when I was a youngster, I did some research and discovered that the active ingredient in Marex was chloroquine, and I was familiar with that drug as it was being used by other public aquariums. Acquiring some myself five years ago, I've begun incorporating it into my arsenal of aquarium fish disease treatments. A few home aquarists have begun re-exploring its uses as well, often calling it by the shorthand name of "CP" which stands for chloroquine phosphate. This article provides those aquarists with additional background information to enable them to be better able to use this "new" drug if they wish - having options is always a good.


Green chromis with Uronema infection that might have responded to chloroquine if treatment was started soon enough.

Chemical properties

Chloroquine was developed for human medicine in the 1930's at Bayer laboratories. It was first thought to be too toxic for any practical use, but decades later, it was shown in clinical trials to have significant value as an anti-malarial drug. However, its subsequent wide-spread use allowed the malaria disease organism to become resistant to it, requiring the development of other treatments.

There are at least three forms of the drug available:

Chloroquine diphosphate (Aralen): C18H26ClN3 . 2H3PO4

Chloroquine hydrochloride (Aralen HCL): C18H26ClN3 . 2HCl

Chloroquine sulfate (Plaquenil): C18H26ClN3 . H2O4S

The Chloroquine base also goes by the name; 7-chloro-4-[[4- (diethylamino)-1-methylbutyl]amino] quinolone. The most commonly available version of the drug for aquarium use is the diphosphate salt. This compound is a fine white fine powder that is readily soluble in water. In dry environments it seems to build up a static charge, and the granules tend to become airborne and then stick to nearby objects. This can create problems when weighing out small amounts of the drug, as it tends to stick to the storage container, the weighing pan as well as nearby objects. Always dissolve the prescribed amount of chloroquine in distilled water before adding it to an aquarium.

English pronunciation of the compound varies between "KLOR-oh-kwin" and "Klor-oh-KWEEN", with the former used by most aquarists, while the latter is listed on some word pronunciation web sites.

Uses and dosages

Chloroquine is typically dosed at a rate of 10 to 20 milligrams per liter (mg/l), with 15 mg/l being considered a "standard dose" (Hemdal 2006). Note: in most instances, solutions measured in "milligrams per liter" are equivalent to "parts per million" or ppm.

The 10 mg/l dose should be used as a quarantine preventative (not for active diseases), or for treating delicate species (although little is known about the sensitivity of different fish species to this medication). A dose of 15 mg/l is considered the normal dose for treating most protozoan infections, while the 20 mg/l dose would be reserved for attempting to eradicate difficult-to-treat Uronema marinum infections.


Hach DR5000 UV spectrophotometer with non-UV DR-2000 on the right.

The first step in preparing to use any drug that will be added to an aquarium at a specific dose is to determine the true water volume of the aquarium. This is often less than an aquarium's advertised volume (or it could be more if there is a sump attached to the system). The most accurate means to determine the volume of an aquarium system is to measure the amount of water it takes to fill the total system, with all decorations in place. As this is usually not possible to do except when the aquarium is first filled, the following method will give accurate enough results in most instances (this method uses US volume measurements combined with metric dosages):

  • Measure (in inches) the length, width and height of the water inside the aquarium from the top of the gravel layer to the water's surface, and inside the glass front to back and side to side. Multiple these three numbers to get the gross volume in cubic inches and then divide by 231 to determine the volume in gallons (there are 231 cubic inches in a US gallon).
  • Deduct an estimated percentage for tank decorations. If you are unsure, the decorations in a typical marine aquarium with artificial coral and rock displace about 15% of the water volume, so you would multiply the gross volume from step 1 by 0.85
  • Use the same technique to measure the volume of the gravel layer (if any), but multiply the result by 0.30, as only about 30% of the gravel layer is water, the rest of the volume is the gravel itself.
  • Use the same technique to measure the volume of the sump (if any).
  • Except for very large systems, the amount of water contained in the filtration system is inconsequential, but you might want to add a couple of gallons to the estimate if the tank uses a large canister filter.
  • Add these measurements together to arrive at the estimated net aquarium volume in gallons.
  • Once you have estimated the aquarium system volume, multiply the number of gallons by the target dose of the drug (in mg/l or parts per million). Dividing this by 266 will give the number of grams of medication that needs to be added to the water.
  • Always run these calculations TWICE to ensure accuracy. If you arrive at different numbers, stop and determine where the mistake was made.


One grave issue when dosing medications occurs if a decimal place is lost through an error in calculation. This can result in a dose many times higher or lower than is called for. Aquarists who are not familiar with using a particular drug may not realize that the dose they have calculated is so far off. For a frame of reference, to dose 100 net gallons of aquarium water with chloroquine at 15 mg/l, you would add 5.6 grams of the drug (100 gal. * 15 mg/l / 266 = 5.639, which rounds down to 5.6 grams of chloroquine).

Home aquarists may have difficulty in measuring minute amounts of a drug to treat small tanks. Avoid guessing or trying to use volume measurements for these weights. Small electronic balances are available for relatively low cost, but may not have sufficient resolution to measure amounts of a drug in the milligram range. One trick to improve accuracy of a measurement is to make a stock solution, and then use a small quantity of that to dose the tank. The reason this works well is that home aquarists generally can measure small volumes of a liquid easier than they can weigh small amounts of a powder. For example, if you need to treat a 10 gallon aquarium with chloroquine at 10 mg/l, you would need to add 376 mg of the drug to the tank, a very small amount to try and weigh out. If you can more easily weigh out a single gram (a nice round amount), you can dissolve that into 12 teaspoons of distilled water, and then add 4 ½ teaspoon of that solution to the 10 gallon tank. For increased accuracy, you can buy a volumetric medicine dosing spoon. These can be used much like a graduated cylinder for measuring accurate amounts of a stock solution. For this example, you would add one gram of chloroquine to 100 milliliters of distilled water, and then add 37.6 ml of that stock solution to the aquarium.


Simple measuring spoons can be used to dose a chloroquine stock solution for smaller aquariums.

Why the concern about such an accurate dosage when chloroquine has a plus or minus 33% margin of error when using the 15 mg/l dose? The reason is that there are two primary chances for error; in the tank volume calculation and when weighing of the drug itself. Two small errors may more or less cancel each other out, but if the errors are in the same direction, they are additive or subtractive and the dose you add to the aquarium could then be outside reasonable limits.

In addition to controlling protozoan parasites, chloroquine also has some use in eradicating certain metazoan (multi-celled) fish parasites. The Georgia Aquarium has used it to control turbellarian worm infestations at a dose of only 10 mg/l (Tonya Claus, personal communication). These worms have been shown to be resistant to treatment with Praziquantel and formalin, so an alternative treatment such as this is much needed.

A single dose of chloroquine at 15 mg/l was found to be effective at eradicating Aiptasia sp. glass anemones within 48 hours. In one test, no reinfestation of these pest anemones was seen in two months following treatment (personal observation). However, this method cannot be used in aquariums housing other invertebrates as this dose also eradicated algae and sponges that were growing alongside the Aiptasia sp. anemones.

In an effort to isolate the drug from sensitive invertebrates, some aquarists have administered the drug orally to their fish. Chloroquine is very bitter, and if the drug isn't masked by strong flavors in the food used to bind it with, fish will soon learn to avoid it. In addition, for oral medications to work, the fish still needs to be feeding normally, and acutely ill fish often refuse to feed. Finally, dosage is very difficult to control in oral medication for aquarium fishes. The drug must be mixed into a gelatin food binder at 6 to 10 milligrams of drug per gram of food, and then that has to be fed to the fish at a rate of around 3% of its body weight per day - and few, if any aquarists know the actual weight of their fishes.

Activated carbon has been widely reported to remove chloroquine from aquarium water at the conclusion of a treatment, but be aware that carbon has been implicated in the development of head and lateral line erosion in marine surgeonfish (Hemdal & Odum 2011). If you do decide to use carbon to remove chloroquine, it would be advisable to use a premium pelleted carbon, rinse it well with deionized water prior to use, and remove all of the carbon when finished. The amount of carbon needed to remove all of the chloroquine will be a guess. A starting point would be 4 to 6 grams of well-rinsed carbon per gallon of aquarium water, placed in a fine mesh bag and added to the aquarium's power filter for 48 hours. If the aquarium will be using delicate invertebrates at the conclusion of the treatment, it would be more prudent to change all of the water first.

There is no test kit to measure the chloroquine concentration in water as there is for many copper medications. Public aquariums and laboratories with access to a UV spectrophotometer can use it to measure chloroquine in the water directly. How this works is that at 329 nm, chloroquine in water absorbs ultraviolet light in proportion to its concentration. Using a quartz cuvette that is transparent to UV, a blank sample of untreated water is first measured. Then, a sample of that water is dosed with a serial dilution of chloroquine in the range to be treated, typically 2.5, 5, 10, 20 and 25 mg/l and the percent transmittance is measured for each sample. Once this standard trend line is graphed, the chloroquine concentration of any water sample within that range can be measured. Because other organic compounds can be present in aquarium water that may also absorb UV light, it is best to create a standard curve for each water system prior to treatment.

In one test attempting to measure the ability of carbon to remove chloroquine, a spiked sample actually showed an increase in absorbance at 329 nm after filtering through carbon for 24 hours. Since the chloroquine level couldn't have risen, it is presumed that something in the carbon dissolved into the water and that obscured the reading. However, this also made it impossible to determine if the carbon actually removed any of the chloroquine, so this aspect remains open to questioning. In a second test, 20 mg of chloroquine was dissolved in a liter of distilled water. This sample was then exposed to 4 g of rinsed activated carbon for a week. Measured at 329 nm, the sample only dropped by a calculated 5 mg/l chloroquine according to the standard curve. Since something in the carbon seems to be obscuring any chloroquine measurements, it is difficult to understand how any of the reports that carbon removes chloroquine could have been substantiated, at least by using a UV spectrophotometer.


An example of four serial dilutions of chloroquine measured on a Hach UV spectrophotometer. The results are % absorbance (the inverse of the % transmittance) at 329 nm. The linear trend line can be used in subsequent tests to measure the amount of chloroquine in aquarium water.

Preliminary in vitro study

Two very basic qualitative in vitro tests were conducted to test the efficacy of chloroquine phosphate as a potential treatment against the ciliate Uronema marinum (Hemdal 2010). Uronema is a fairly common ciliate that is difficult to treat as these parasites can burrow into the fish's skin and therefore isolate themselves from many external bath treatments such as formalin, copper and hyposalinity. These informal tests show that this drug is effective at killing Uronema when it is used as a bath, but it is unknown if enough of the drug would taken up by the fish in order to raise the level in the blood to therapeutic levels.

In the first test, the body of a small parrotfish fish that had succumbed to a Uronema infection was cut in half. One section of the fish was placed in tank water, the second section was placed in tank water dosed with Chloroquine at 40 mg/l (a higher than normal dose). After six hours, the number of Uronema in the treated sample had been markedly reduced, while the numbers in the untreated sample had actually increased.

In a second test, the bodies of two green chromis that had died from acute Uronema infections were exposed to chloroquine at 35 mg/l. A marked reduction of the numbers of the ciliate was seen within three hours, and only one surviving Uronema was seen on the body of one of the fish after eight hours. Using deceased fish for these bio-assays is problematic in that there is difficulty obtaining specimens "as-needed" and room temperature tests longer than 24 hours cannot be performed as the fish flesh begins to putrefy.


At doses typically used to treat fish diseases, chloroquine is also toxic to many invertebrates, algae and bacteria. Seriously high ammonia levels ( > 1 mg/l NH3) are sometimes seen a few days to a week after dosing an aquarium with chloroquine. It is unknown why this is seen in some aquariums but not others. One hypothesis is that the chloroquine has a direct antibiotic effect on the nitrifying bacteria. Another idea is that the chloroquine kills so much microscopic life in the aquarium that the beneficial bacteria are overwhelmed, and an ammonia spike develops. Most likely, it is a combination of both of these factors causing this issue. Always monitor the ammonia levels in aquariums during treatment with chloroquine. Freshwater aquariums should also be monitored for subsequent rise in nitrite levels as well.

Ultraviolet light seems to alter the chemical make-up of chloroquine in water. This is particularly a concern when UV sterilizers are employed. The UV light causes changes in the chloroquine that can turn the aquarium water a murky brown (Tiffany Adams, Shedd Aquarium, personal communication). The presumption is that the effect of the drug is also altered, so UV sterilizers (and probably ozone generators) must be turned off during treatment. Some aquarists go to the extreme of blocking all light entering the aquarium during treatment, but this is not necessary unless the aquarium is open to natural sunlight.

As mentioned, the use of chloroquine to treat malaria in humans has long been known to lose effectiveness as the Plasmodium protist that causes the disease developed a resistance to the drug. Purely speculation, but the same mechanism could cause resistance to aquarium disease-causing protists as well. If this problem ever develops, it will most likely appear in public aquariums or fish importers as they use the drug repeatedly in the same centrally filtered systems. Home aquarists are unlikely to administer the high number of treatments required to cause such a resistance to develop.
The Material Safety Data Sheet (MSDS) for chloroquine phosphate is difficult to interpret. Much of the toxicity data listed were derived from chronic exposure in humans taking the drug for control of malaria; retinal damage, nervous system disruption, and liver damage. Acute exposure of the amounts typically used in home aquariums can cause irritation to the eyes and respiratory tract. Always use gloves, eye protection and a dust mask when handling this material, and keep it away from children and pets.

The Phosphate Connection

Most, if not all of the chloroquine available for aquarium use is in the form of chloroquine diphosphate (as opposed to chloroquine hydrochloride or sulfate). This means that dosing an aquarium with this drug will also add some phosphate (PO4) to the water when the compound dissociates as it dissolves. Theoretically, using the molecular weights of its components, chloroquine will release about 20% of its weight as PO4 . This means that for a typical 20 mg/l dose of chloroquine, one would expect the phosphate level in the aquarium to rise by around 4 mg/l. Empirically, a series of tests on chloroquine at 20 mg/l in distilled water resulted in a concurrent rise in PO4 of 4 to 6.1 mg/l, a bit higher than expected*. A rule of thumb might be that for any dose of chloroquine, you could expect to see a rise in phosphate levels of around 20 to 30% of the total dose of chloroquine. Therefore, a single dose of chloroquine at 10 mg/l would increase the PO4 concentration in the water by about 2 to 3 mg/l. This is would be a major concern in reef aquaria, but as chloroquine is typically used in fish-only aquariums, or quarantine systems, the residual phosphate is less of an issue and can be reduced by water changes.



The current major drawback to using chloroquine to treat fish diseases is locating a commercial source of the drug. Public aquariums, buying large quantities, have no difficulty in acquiring it from online companies at around $185 per kilogram. Hobbyists, needing much less of the drug, have not been able to find it easily available in lesser amounts - but that should be changing, now that its use has become more popular again. Until an aquarium manufacturer starts marketing it again, you may be able to acquire it from your veterinarian, or perhaps go in for a "group buy" with other hobbyists. Recent online prices for non-prescription chloroquine vary depending on the amount purchased from .185 cents per gram up to $2.40 per gram. One gram of chloroquine will dose 18 gallons of water at 15 mg/l.


While not a panacea or miracle drug, chloroquine is experiencing resurgence in popularity for use in fish-only aquariums and quarantine systems to treat a variety of problems ranging from Cryptocaryon to Aiptasia anemone infestations. Chloroquine remains active in aquariums for many weeks, seems to have low toxicity to fish and may be removed using activated carbon. In critical applications, treatment levels can be measured with a UV spectrophotometer, and the dose adjusted accordingly.


  1. Hemdal, J.F. Odum, R.A. 2011. The Role of Activated Lignite Carbon in the Development of Head and Lateral Line Erosion in the Ocean Surgeonfish. North American Journal of Aquaculture 73:4, 489-492
  3. -- 2009. Mortality Rates of Fishes in Captivity. Advanced Aquarist's Online Magazine. 8(12):
  4. -- 2006. Advanced Marine Aquarium Techniques. 352pp. TFH publications, Neptune City, New Jersey

No publisher Jay Hemdal Pomacanthus Publications, Inc. Fish Medication Aquarium Fish Jay Hemdal 2013-02-20T16:00:00Z Page








A Milwaukee MR100ATC refractometer used in this study.


Instant Ocean Hydrometer.

Refractometer Result Notes

pH Kits



A typical Salifert pH test kit utilized in this study.

pH Kit Result Notes

Nitrate Kits



A Red Sea Nitrate Pro test kit.

Nitrate Kit Result, ppm Notes

Calcium Kits



API Calcium Test Kit.

Calcium Kit Result, ppm Notes

Alkalinity Kits



Seachem MultiTest for pH and Alkalinity.

Alkalinity Kit Results, meq/l Notes





Alkalinity Kits - Part II








Freshwater, meq/l
Nutrafin 2.80 2.80 2.80 2.80 2.80 2.80 2.80
Salifert 4.00 4.00 4.00 4.00 4.00 4.00 4.00
Seachem 4.00 4.00 4.50 4.00 4.00 4.50 4.17
Red Sea 3.60 3.60 3.60 3.60 3.60 3.60 3.60
API 3.60 3.60 3.60 3.90 3.90 3.90 3.75
Instant Ocean 3.50 3.50 3.50 3.50 3.50 3.25 3.46
Saltwater, meq/l
Nutrafin 2.80 2.80 2.80 2.80 2.80 2.60 2.77
Salifert 3.60 3.60 3.70 3.60 3.60 3.60 3.62
Seachem 4.00 3.50 3.50 4.00 4.00 4.00 3.83
Red Sea 2.80 2.70 2.70 2.90 2.80 2.70 2.77
API 3.90 3.60 3.60 3.90 3.60 3.60 3.70
Instant Ocean 3.50 3.50 3.50 3.25 3.25 3.25 3.38



API: This kit had no expiration date indicated.


Red Sea: This kit was not expired.



Seachem: This kit had no expiration date indicated.


Salifert: This kit was not expired.


Nutrafin: This kit was not expired.

More Comments





  3. Wikipedia, 2012. Color blindness. URL:

Product Review: Hanna 'Checkers': Calcium and Iron Colorimeters and Thoughts on Aquarium Industry Product Quality Control Both instruments are recommended if the minimum and maximum detection limits meet your requirements and good laboratory practices are maintained. Good job Hanna! Click through to see the images.





Hanna Iron Checker

What is a Colorimeter?


Importance of Calcium and Iron in the Aquarium


Hanna Instruments


Instrument Programming


Manufacturer's Specifications: Iron



Manufacturer's Specifications: Calcium

Marine Calcium Colorimeter (Model HI-758):

  • Manufacturer's Specifications Range: 200-600 mg/L
  • Resolution: 1 mg/L
  • Accuracy: ±6%
  • LED Maximum Wavelength: 610nm
  • Temperature: 0-50C (32-122F)
  • Humidity: 95% non-condensing
  • Battery: 1 AAA
  • Auto Shut-off after 10 minutes of non-use
  • Weight: ~2 ounces


Possible Interferences with the Zincon Calcium Analysis Method


Testing Protocol























  • Instrument Price
  • Good Accuracy for the price, especially for iron
  • Calcium reagents are marked with an expiration date
  • Built-in timer (iron only)
  • Instrument Error Messages
  • Material Safety Data Sheet (MSDS) available on-line
  • Hanna offers optional calcium and iron standards for quality assurance


  • Cuvettes are tall and easily tipped over
  • Calcium test requires use of deionized water that is not supplied

Bottom line


Suggested Retail Price


Optional Accessories


Other Instruments from Hanna


  • A Magnesium Checker is under development

Contact Information



Or write to:

Hanna Instruments, Inc.
584 Park East Drive
Woonsocket, RI 02895

Testing Procedures and Suggestions





The Meniscus




An Inexpensive Cuvette Holder


Tips on Sampling and Testing


Sample Preservation Methods for Calcium and Iron




Waste Disposal


Thoughts of Product Quality Control in the Reef Aquarium Industry



In Closing

All items tested were obtained through normal retail channels.


No publisher Dana Riddle Pomacanthus Publications, Inc. Hanna Calcium Hach Iron Chemistry 2012-04-18T15:00:00Z Page
Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both Foods are by far the most important source of phosphate in most aquariums. In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize. Click through to see the images.


Phosphate is an ion of great concern to reef aquarists. In fact, aside from calcium and alkalinity, it is probably the chemistry topic on which reef aquarists focus the most. Much of this concern is warranted, with phosphate potentially contributing to algae problems, poor coloration of corals and other invertebrates, and growth of most photosynthetic organisms. For these reasons, every reef should have a plan for export of phosphate in one or more ways, and the choices abound. Topics relating to desired target levels and the many export methods have been covered in detail by me and other authors in the past, and I won't dwell on them here.

What I will focus on relates to the various sources of phosphate in reef aquaria, and how important each one actually is to an operating aquarium. There have long been numerous misunderstandings of these source issues, but in the last two years it seems that these misunderstandings have become more common and are sometimes driving aquarists to unwarranted actions.

In part, I attribute this recent uptick in confusion to the newly available phosphate checkers from Hanna. Without getting into any discussion of their relative accuracy or the merits of using them, I think many aquarists are being lured into inappropriate actions by finding phosphate in various additives that they were not aware of previously. To paraphrase Field of Dreams: "Build it and they will find phosphate". In order for aquarists to interpret what these found values mean, they need to have an understanding of the overall phosphate balance in coral reef aquaria. This article strives to provide the understanding necessary to put phosphate issues into proper perspective.

So just for starters, let's see how many of you would be concerned by each of these scenarios:

  1. My purified fresh water I use for top off has 0.05 ppm phosphate in it. Since I'm trying to keep my tank at 0.02 ppm, that's obviously too much. What should I do?
  2. I put a cube of my frozen fish food in a half cup of water and did a phosphate test on the water. I got a whopping value of 1.0 ppm!!! That's a huge problem, right?
  3. I put a teaspoon of my GAC (granular activated carbon) in a glass of fresh water, and then tested the water for phosphate. It was dark blue and I could not even get a reading there was so much. Time to look for another brand, right?
  4. I know I feed my fish and corals, but I carefully rinse my foods, use only frozen foods, and only feed enough that all is eaten. So I have no idea where my phosphate is coming from. Must be my RO/DI isn't working as there is no other possible source.

Experience tells me that 95% or more of reef aquarists agree that the first three are problems to be solved, and at least half have the same feelings as expressed in number four. In reality, the first three are really not substantial issues at all and reefers need to understand why. Scenario four sums up the main point reefers need to understand: foods are the primarily source of phosphate in almost any aquarium that is being fed, regardless of the choice of foods and rinsing etc. In most aquaria, this source dominates all other sources by a factor of ten to a hundred or more, even if scenarios 1-3 are also true!

Food Sources of Phosphate

In order to begin to understand phosphate sources in aquaria, let's first look at foods. Contrary to what many suppose, phosphate is not something that can be avoided in a nutritious fish food. Phosphorus is present in many of the biomolecules of life, so every natural tissue that goes into a fish food will have substantial phosphorus in it. Phospholipids make up a substantial part of cell membranes. The genetic code of every organism is made of DNA, and that DNA contains a phosphate bridge between each base pair (Figure 1 shows how much phosphate is really in DNA). The way that all cells get energy is through conversion of ATP to ADP, and these molecules contain 3 and 2 phosphate moieties respectively (Figure 2).


Figure 1. The structure of DNA as drawn by Madeleine Price Ball for Wikipedia. Phosphorus is shown in yellow.


Figure 2. The structure of ATP showing the three phosphate moieties on the left hand side.

Most importantly for nutritional aspects of foods and phosphate, proteins contain phosphate. Many budding chemists understand that proteins are made of amino acids, and none of the standard amino acids contain phosphate, so where does the phosphate come from? It turns out that organisms attach phosphate to the hydroxyl group of the amino acids threonine and tyrosine in proteins to turn on and off many types of protein functions. Consequently, proteins often contain a lot of phosphate, making it very hard to make nutritionally complete foods without substantial phosphate. The relationship between phosphate and protein is so tight that people who suffer from excess phosphate (typically those with kidney disease, and especially those on dialysis) are unable to get enough protein without getting too much phosphate. These patients take oral phosphate binders to bind dietary phosphate before it is absorbed from their small intestines because restricting dietary phosphate just is not effective enough.

Quantitation of Phosphate in Foods

How much phosphate is in foods? A lot, but it does depend on the food. Some aquarium foods state on the label a minimum specified amount of phosphorus (phosphorus is the atom, P, at the center of a phosphate ion, PO4---). Analyses of foods often quote an amount of phosphorus instead of phosphate as the unit of measure. Like feet and inches, these are just different units of measure of the same thing, and values of phosphorus are multiplied by 3.1 to get values to phosphate.

For foods that are intended for human consumption (such as shrimp or clams), we can look up known data on phosphorus content. Unfortunately, many manufacturers of aquarium foods do not supply phosphorus values and they are complex mixtures of many ingredients which preclude us from looking them up. Perhaps some manufacturers are concerned about scaring aquarists about the phosphate content. Fortunately, Ron Shimek analyzed a variety of foods several years ago and this data set can also be used to understand how much phosphorus is in various commercial aquarium foods. Tables 1-3 contain data on the phosphorus and protein content of many aquarium foods, with Table 1 containing dry foods, Table 2 containing frozen foods, and Table 3 containing grocery store foods that are sometimes used in aquaria.

These raw phosphorus values alone allow us to know how much phosphorus is entering the aquarium by feeding a certain food, and we will use these numbers in several analyses later in this article. One must be wary of relying too much on such numbers for comparative purposes, however, since some foods have substantially more moisture or fillers in the food, which serve to drop the percent phosphorus, but are not necessarily better choices from a phosphorus standpoint. One simply needs to feed more of a wetter food than a drier one to attain the same total nutrition, offsetting the lower claimed phosphorus value.

One useful way to compare foods to each other is by comparing the phosphorus to protein ratio. In this crude way, we can eliminate effects due to moisture and fillers. Obviously this method has its own flaws since the nutritional value of foods is far more complex than a protein value alone provides, but it will allow us to understand among similar types of foods, which ones seem to provide more or less phosphorus. In order to help guide the reader, I have chosen to show the higher phosphorus to protein foods in red and the lower ones in green in Tables 1-3. The cutoff values I used are completely arbitrary, and one should definitely not make a choice of food based on this criterion alone. Nevertheless, several points are apparent:

  • Dry and frozen foods vary substantially in phosphorus to protein content. There are high and low phosphorus foods in both categories. On balance, one could not say from this data that typical dry foods are any worse in this regard than are typical frozen foods.
  • With the exception of seaweeds, grocery store foods do generally seem to have a lower phosphorus to protein ratio than many other choices, although several Ocean Nutrition frozen foods are similarly low. This presumes that one is using grocery store foods that are not treated with phosphate to preserve freshness in the processing plant, but that is a concern for many of these materials.
  • Shrimp seem to be a standout in terms of a low protein to phosphorus ratio for grocery store foods.
  • Fish with bones have a high phosphorus content, since bones are modified calcium phosphate, but whether these bones are fully digested or not probably depends on what eats them and how long one otherwise waits for them to decompose.
Table 1. Phosphorus and protein content of some common dry aquarium foods.
Food Protein (mg/g) Phosphorus (mg/g) Phosphorus/Protein(w/w) Source of Data
Brine Shrimp Direct Golden Pearls 550 15 0.027 Shimek
Brine Shrimp Direct Plankton Gold Flakes 490 8.3 0.017 Shimek
Cobalt Aquatics Brine Shrimp Flakes 440 10 0.023 Label
Cobalt Aquatics Spirulina Flakes 450 10 0.022 Label
IO Marine Chips Herbivore 460 9 0.020 Label
IO Marine Chips Omnivore 460 11 0.024 Label
IO Marine Grazing Block 40 0.5 0.013 Label
IO Marine Pellets Herbivore 440 10 0.023 Label
IO Marine Pellets Omnivore 470 12 0.026 Label
IO Seaweed Grazing Blocks 25 0.3 0.012 Label
Nutrafin Max Marine Angel Sinking Pellets 440 8 0.018 Label
OSI Marine Flake 470 6 0.013 Label
TetraAlgae Vegetable Enhanced Crisps 460 10 0.022 Label
TetraMarine Flakes 460 12 0.026 Label
TetraMarine Granules 440 14 0.032 Label
Vibragro Saltwater Staple 300 15 0.050 Shimek
Table 2. Phosphorus and protein content of some common frozen aquarium foods.
Direct Tahitian Blend Cryopaste 44 1.4 0.032 Shimek
Frozen Plankton/Krill Brine Shrimp 88 1.6 0.018 Shimek
Gamma Foods Lancefish 180 4.4 0.024 Shimek
Hikari Bio-Pure Clam On A Half Shell 32.9 3 0.090 Label
Hikari Bio-Pure Clam On A Half Shell (meat only) 128.4 4.1 0.032 Label
Ocean Nutrition Frozen Formula 1 160 1.1 0.007 Shimek
Ocean Nutrition Frozen Formula 2 62 1.2 0.019 Shimek
Ocean Nutrition Frozen mysis 52 0.1 0.002 Label
Ocean Nutrition Frozen Prime Reef 130 0.9 0.007 Shimek
Oregon Desert Brine Shrimp Company Silversides 42 4 0.095 Shimek
San Francisco Brand Frozen Brine Shrimp 31 0.72 0.023 Shimek
Table 3. Phosphorus and protein content of some common grocery store foods used in reef aquaria.
Broccoli 30 0.66 0.022 analysis
Clams (no shell) 128 1.69 0.013 analysis
Clams (no shell) 128 1.69 0.013 analysis
Cod 179 1.74 0.010 analysis
Cod 229 2.23 0.010 analysis
Eel 184 2.16 0.012 analysis
Eel 186 2.16 0.012 analysis
Kelp 17 0.42 0.025 analysis
Mackerel 186 2.17 0.012 analysis
Mussel 119 1.97 0.017 analysis
Nori 290 6.4 0.022 Shimek
Octopus 149 1.86 0.013 analysis
Oyster (no shell) 70 1.35 0.019 analysis
Oyster (no shell) 71 1.35 0.019 analysis
Salmon 204 2.4 0.012 analysis
Sardine 209 3.66 0.018 analysis
Scallops 168 2.19 0.013 analysis
Shrimp 209 1.36 0.007 analysis
Shrimp 210 0.7 0.004 analysis
Spirulina 59 1.1 0.019 analysis
Squid 156 2.2 0.014 analysis
Wakame (seaweed) 30 0.8 0.027 analysis

Impact of Foods on the Aquarium Phosphate Balance

Now we come to the heart of the issue. The actual amount of phosphorus present in foods and what it means. In order to understand the effects of foods, we need to understand what happens to them when added to an aquarium. Some aquarists are under the misconception that eaten foods do not contribute to the free phosphate in the water. Many aquarists are told the mantra of feeding only as much as is eaten, and they confound this idea with the assumption that when doing so, one minimizes the phosphate release. That idea is simply untrue.

A fish or other organism that eats foods takes in substantial phosphate, as shown above. But what happens to it? If the organism is not actually expanding in size (such as an adult green chromis, or a person), the phosphate that is taken in is almost entirely excreted back into the water. The only exception to that process is the very small amount of phosphorus that goes into eggs or sperm, and since in most aquaria those items are rapidly consumed by other organisms, the phosphorus will ultimately get into the water.

Growing organisms do take up a small amount of phosphorus from the diet and retain it in their growing tissues, but the emphasis is on small. A study of a fish farm with rapidly growing rainbow trout in the ocean showed that 78-82% of the phosphorus feed to the fish was lost to the environment. A second aquaculture study using normal fish foods showed that 62% of the fed phosphate was released to the environment, with 35% being released as soluble phosphate available directly to algae, and 27% as phosphorus in fecal pellets (which if not removed, will break down in an aquarium releasing the phosphate again). Another study showed that 81.5% of commercial diet phosphate was released to the environment, but that with a "special" diet with low phosphate and low fish meal this could be reduced to 64% lost. A fourth study showed that growing fish fed slightly less phosphate than they need (to optimize theoretical uptake) take up and retain different phosphate sources differently. Using a purified protein diet, they observed retention of 72% of the phosphorus, 51% retention of phosphorus from added fish bone meal, and higher levels of uptake and retention for inorganic phosphate supplements (such as sodium phosphate).

This sort of study is of concern in aquaculture settings due to environmental contamination due to the released phosphorus and nitrogen. To my knowledge, however, it has never been done in a reef aquarium. Such phosphorus balance studies have also been performed in people for many years. In adults it is clear that nearly all phosphate taken up is excreted, mostly in the urine and some in the feces. Even in young growing children, the amount of phosphorus retained from the diet is only 5-20% of that consumed, with 80-95% excreted in the urine and feces. While such studies are fairly far removed from reef aquaria, they do supporting the idea that organisms take in a lot more phosphorus than they retain, even when growing.

Consequently, reef aquarists should expect that much of the phosphorus added to a reef aquarium in the form of foods ultimately ends up in the water as phosphate. Whether that portion getting into the water is 95% or 35% won't substantially impact the conclusions below that foods add a very large amount of phosphate.

Quantitation of the Food Impact Aquarium Phosphate

Using the assumption that most of the phosphorus present in foods ultimately ends up as phosphate in the aquarium, we can calculate roughly what that effect is. Even if the actual number is a half or a quarter of that added, getting the ballpark information is very useful to gauge the importance of this phosphate source. Obviously the calculated value depends on how much of what is fed to what size aquarium.

Table 4 shows a variety of possible feeding schemes that an aquarist might use on a hypothetical 100 gallon (379 L; actual water volume) aquarium. Aquarists can decide for themselves how these regimens compare to their own feed schedules.

Table 4. Phosphate additions to a 100 gallon actual water volume aquarium with different daily feeding regimens.
Foods Fed Phosphorus Added Daily (mg) Equivalent Phosphate Added Daily (mg) Equivalent Phosphate Concentration Added Daily (ppm)
1 Prime Reef Cube 2.7 8.4 0.022
1 Prime Reef Cube1 Formula 1 Cube 6.0 18.6 0.049
1 Formula 2 Cube1 Mysis Cube 3.9 12.1 0.032
IO Marine Omnivore Chips (2 g) 22 68 0.18
IO Marine Omnivore Chips (1 g)Silversides (1/2 teaspoon)Nori (2.5 g = large sheet) 37 115 0.30

Obviously there is a big range depending on how much is fed. What is surprising to many folks, however, is how large that number is relative to typical target levels of phosphate in reef aquaria, which might be something like 0.03 ppm or less. Even the light feeding of a single cube of a relatively low phosphate frozen food to this aquarium supplied most of that target amount in a single feeding. Heavy feeding added ten times that amount in a single day. In short, this high daily addition rate is why phosphate control is often very difficult or reef aquaria.

Rinsing Foods and the Effect on Phosphate

Now that we have some information on the phosphate in foods, we can critically examine the concern that many aquarists have about foods, and specifically their rinsing of frozen foods before use. A typical test you see is someone taking a cube of fish food, thawing it, and putting it into a half cup of water. They then test that water for phosphate and find it "off the charts". Let's assume that means 1 ppm phosphate, which would give a very dark blue color in many phosphate tests. Bear in mind this is a thought problem, not an actual measured value, but it is typical of what people think the answer is.

Is that a lot of phosphate? Well, there are two ways to think of the answer.

The first way is as a portion of the total phosphate in that food. A half cup of water at 1 ppm (1 mg/L) phosphate contains a total of 0.12 mg of phosphate. A cube of Formula 2 contains about 11.2 mg of phosphate. So the hypothetical rinsing step has removed about 1 percent of the phosphate in that food. Not really worthwhile, in my opinion, but that decision is one every aquarist can make for themselves.

The second way to look at this rinsing is with respect to how much it reduces the boost to the aquarium phosphate concentration. Using the same calculation as above of 0.12 mg of phosphate, and adding that to 100 gallons total water volume, we find that phosphate that was rinsed away would have boosted the "in tank" phosphate concentration by 0.12 mg/379 L = 0.0003 ppm. That amount washed away does not seem significant with respect to the "in tank" target level of about 50-100 times that level (say, 0.015 to 0.03 ppm), nor does it seem significant relative to the total amount of phosphate actually added each day in foods (which is perhaps 50-1000 times as much, based on input rates from Table 4. Again, the conclusion I make is that rinsing is not really worthwhile, in my opinion.

Comparison of Food Sources of Phosphate to Other Sources

What about other sources of phosphate, like the "crappy" RO/DI water containing 0.05 ppm phosphate? A similar analysis will show it equally unimportant relative to foods.

Let's assume that the aquarist in question adds 1% of the total tank volume each day with RO/DI to replace evaporation. Simple math shows that the 0.05 ppm in the RO/DI becomes 0.0005 ppm added each day to the phosphate concentration in the aquarium. That dilution step is critical, taking a scary number like 0.05 ppm down to an almost meaningless 0.0005 ppm daily addition. Since that 0.0005 ppm is 40-600 times lower than the amount added each day in foods (Table 4), it does not seem worthy of the angst many aquarists put on such measurements. That said, tap water could have as much as 5 ppm phosphate, and that value could then become a dominating source of phosphate and would be quite problematic. Purifying tap water is important for this and many other reasons.

The same sort of calculation applies to analyzing other phosphate issues, such as the GAC in scenario three. The issue of finding "high" phosphate in GAC soaked in fresh water was frequently quoted as a reason to use one or the other brand of GAC, and probably still is. But simple analysis as shown above for the food rinsing puts the lie to this being a big problem.

One needs to consider how much GAC one will really use in the aquarium and how often it is added in order to interpret how important the added phosphate is. A typical recommendation might be 1 cup of GAC per 100 gallons of aquarium water, and to change it in 4-6 weeks. Let's assume we detect 0.5 ppm phosphate when a teaspoon is placed in a cup of water, and we get scared by the dark blue color during the test. Is this reasonable? That 0.5 ppm from a teaspoon in a cup of water translates to 0.015 ppm phosphate when a cup is used in 100 gallons.

That 0.015 ppm may be significant, being a typical target concentration level for reef aquaria and amounting to about half to a twentieth of the amount added daily in foods, but remember, it is used for 4-6 weeks. During those 4-6 weeks before the next replacement, foods add 50-700 times as much phosphate. So while it is not unreasonable to look for another brand of GAC, to blame phosphate or algae issues in the aquarium on its use would stretch credibility because it is a very tiny portion of the total phosphate being added.


Foods are by far the most important source of phosphate in most aquariums. While there are big variations between foods, it does not appear in this analysis that dry foods are the nasties they are often made out to be, relative to frozen foods. There are better and poorer choices (with respect to phosphate) to be made within each food type. Avoiding foods with bones, however, might be worthwhile if delivering less phosphate is a goal. Additionally, fresh grocery store shrimp seems to be one of the best foods from this standpoint.

In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize. It can be scary to learn that your purified fresh water has phosphate in it, or that your salt mix has detectable phosphate, or that your supplements or whatever have some phosphate. But just because you detect something, and maybe you even detect a concentration far higher than in your aquarium, that does not by any means imply that those sources are significant enough to warrant some sort of corrective action. Our analytical tools have become fairly sensitive, allowing us to detect things which might sound like trouble, but really aren't. We need to understand the various dilution issues involved as well as the overall phosphate balance in a reef aquarium to evaluate the importance of different measurements.

Just use some math and put it all into perspective, before using some dollars or time to chase a trivial "problem".

Happy Reefing

No publisher Randy Holmes-Farley, Ph.D. Pomacanthus Publications, Inc. Food Chemistry And The Aquarium Phosphate Aquarium Chemistry Phosphates Chemistry Randy Holmes-Farley 2012-03-21T13:00:00Z Page
Feature Article: Spectral Distributions of LEDs: AI-Sol, Radion, Orphek, EcoRay, Mvava In addition to the characterization of light by its intensity and distribution, the spectral distribution is also of interest. Light sources emit light at varying amounts at different wavelengths. Spectral distribution characterizes the light output across different wavelengths of the light spectrum. Click through to see the images.



  • Violet - 400 to 440nm
  • Blue - 440 to 490nm
  • Green - 490 to 540nm
  • Yellow - 540 to 590nm
  • Orange - 600 to 650nm
  • Red - 650 to 700nm






Figure 1: Example of a Spectral Power Distribution plot


Methods and Approach


Table 1: LED Fixtures evaluated for Spectral Output
Radion X30
Orphek PR-156
Ecoray 112
Aquaillumination SOL White
Aquaillumination SOL Blue
Aquaillumination SOL Warm White

Radion XR30W




Figure 2a. Spectral Output of the different LED components - Radion XR30W



Orphek PR-156



Figure 3a. Spectral Output of the different LED components - Orphek PR-156



Ecoray 112

Similar to the Ecoray 60 in design, this is the larger version with 112 LEDs - 56 White High Power 1 Watt LED, (color temperature 12000K - 160000K) and 56 Blue Actinic High Power 1 Watt LED (Wave Length 450-460 nm) arranged in a 8X14 grid. The white and blue LEDs can be controlled separately, only in 2 states ON or OFF. The spectral output for the different channels and all LEDs ON is shown in figure 4a along with the comparison to metal halide in figure 4b.


Figure 4a. Spectral Output of the different LED components - Ecoray 112






Figure 5a. Spectral Output of the different LED components - Mvava II



Aquaillumination - SOL White



Figure 6a. Spectral Output of the different LED components - AI Sol White



Aquaillumination - SOL BLUE



Figure 7a. Spectral Output of the different LED components - AI Sol Blue



AI Nano Sol (with warm white)



Figure 8a. Spectral Output of the different LED components - AI Sol Nano







Figure 9.




No publisher Sanjay Joshi Pomacanthus Publications, Inc. LED Ecotech Aqua Illumination Spectrum Lighting Orphek Sanjay Joshi, Ph.D. Ecoray Mvava Radion 2012-03-07T15:00:00Z Page
Aquarium Chemistry: Effects of GFO (Granular Ferric Oxide) on 'Trace' Metals Concentrations in Artificial Seawater Granular Ferric Oxide (GFO) is popular among reef hobbyists as a means to decrease phosphate levels and subsequently algal growth in their tanks. GFO, however, can also affect other ions and compound levels as well. In this article, Dana investigates the effect that GFO has on our tanks outside of decreasing phosphate levels. Click through to see the images.


Use of Granular Ferric Oxide (GFO, or iron oxide hydroxide) is a popular and effective means to reduce reactive phosphate (a non-metal) concentrations in aquaria hence reducing the potential for algal growths. Silicate (a metalloid) is also efficiently removed. It is known that GFO can also remove a number of transition metals (such as zinc, copper, manganese, etc.) but few experiments have been conducted on the removal (or addition) of metals, non-metals, and metalloids from/to seasoned artificial seawater. This article will examine the results of recent testing and discuss the implications for reef hobbyists.

In an attempt to consolidate information, data concerning phosphorus and silica removal as well as alkalinity are included, previously published here:


Before proceeding, a review of terms used in this article will be defined:

A measure of a liquid's ability to resist shifts to lower (acidic) pH values. Alkalinity can be composed of carbonate, bicarbonate, and/or hydroxide as well as borate, silicate, phosphate and other bases. Reported as milligrams per liter calcium carbonate (CaCO3 ).
Combining a metallic ion with an organic substance (such as EDTA - ethylenediaminetetraacetic acid - or perhaps with naturally-occurring aquatic humic substances). By doing so, the metal stays in solution and may be 'bio-available'. A chelated substance can also be called complexed.
Cobalt (Co)
Cobalt is an essential trace element for algae, some bacteria and animals (but not higher plants). Cobalt is a transition metal and is found at very low concentrations (0.003 to 0.4 ppb) in natural seawater.
Copper (Cu)
Copper is an essential trace element for plants and animals. By law, copper cannot exceed 1.5 mg/L in 10% of homes served by larger potable water systems. Copper levels can exceed this maximum allowable limit when aggressive (corrosive) water degrades copper piping and fixtures. Copper is a transition metal and low concentrations are toxic to invertebrates and is often found in natural seawater at concentrations of ~0.001 to 0.01 mg/L.
This is a technique used to break down a substance into components that can be analyzed. Digestion usually involves exposing the substance to high temperature and strong acids and is necessary in order to accurately access concentrations of metals chelated with organic substances. However, vigorous digestion is not always required in order to estimate total metals (such is the case for Hach's iron and copper chemistries).
Iron (Fe)
Iron is absolutely required for growth and well-being of plants and animals. The EPA has set a secondary limit (suggested, but not enforceable) on concentrations of iron in drinking water at 0.3 mg/L. High iron concentrations in drinking water can cause staining of plumbing and clothes as well as impart objectionable taste and color to food. Iron is a transition metal. Ocean water contains 0.002 to 0.02 mg/L iron.
Manganese (Mn)
Manganese is an essential element for plant and animal growth. Its concentration should not exceed 50µg/L (U.S. EPA secondary standard for potable water) and elevated concentrations can stain plumbing, cooking utensils and clothing. Manganese is a transition metal. Previous research suggests manganese can be effectively removed by GFO. Seawater contains 0.001 to 0.01 mg/L.
Milligrams per liter, essentially the same thing as parts per million (ppm).
Nickel (Ni)
Nickel is suspected to be an essential element for at least some plants and animals. The EPA has established a primary, enforceable limit of 0.1 mg/L in drinking water. Nickel is a transition metal and naturally occurs in seawater at ~0.0001 mg/L. Hach's reagents allow determination of cobalt and nickel through analyses of a single sample. Since the protocol did not include spiking of samples with nickel, it is not surprising that nickel levels fell below the detection limit of the instrument (data not shown).
The intensity of the acidic or basic character of a solution.
Phosphorus (P)
Phosphorus occurs in water almost exclusively as phosphate (PO43-). Excessive amounts of reactive (or ortho-) phosphate encourages algal and plant growth but can be a limiting nutrient at low concentrations. Phosphorus is essential to all living organisms. Phosphorus is a non-metal.
Silicon (Si, as SiO2)
Silicon is required for proper function by some plants and animals. It is used by diatoms to produce skeletons and is sometimes not included in the formulation of artificial seawater. There is no limit established by the U.S. EPA on silicates in drinking water. Silicon is a metalloid.
Zinc (Zn)
Zinc is an essential element for growth in plants and animals but elevated levels may be toxic. The U.S. EPA has established a level of no greater than 5 mg/L in drinking water. Deterioration of galvanized pipe and brass fixtures can add zinc to drinking water and can cause a bitter taste. Zinc is required in the genetic make-up of every cell and is an absolute requirement for all biologic reproduction including DNA and RNA syntheses. Zinc is an integral component of about 200 metalloenzymes, including carbonic anhydrase, superoxide dismutase, alcohol dehydrogenase, carboxypeptidase, glutamic dehydrogenase, lactic dehydrogenase, and alkaline phosphatase as well as hormones. Zinc is a transition metal and has been shown to be adsorbed by GFO regardless of the solution's ionic strength. Zinc is found in seawater at a level of ~0.005 mg/L.



Most instructions for use of iron-based materials used in phosphorus removal will caution the end-user of potential drops in aquarium water alkalinity.


Figure 1. Effects of GFO on alkalinity (as mg/L CaCO3).

As expected, alkalinity was affected by the addition of GFO (see Figure 1). Hobbyists should be aware that many substances will impact alkalinity levels, including two that these GFO products removal effectively - phosphorus and silica!


Cobalt is found in natural seawater at parts per billion concentrations. Under the conditions of this procedure, cobalt (likely only free cobalt) is actively removed by GFO. See Figure 2.


Figure 2. Cobalt concentrations fell after GFO was introduced.

Copper (Free)

Copper in an aquarium is a double-edged sword. It is an essential trace element but is toxic at higher concentrations. Free and total copper were determined. See Figures 3 and 4.


Figure 3. Free copper removal by GFO. The Detection Limit of the test is 0.02 mg/L as Cu. The final reading (0.09 mg/L) is still above that usually seen in natural seawater.

Copper (Total)

Total copper is the sum of free and complexed copper.


Figure 4. Total copper fell due to removal of free copper by GFO.

Copper (Chelated or Complexed)

Copper, complexed with organic substances, can be determined by subtracting free copper from total copper. Figure 5 shows complexed copper is weakly removed, if at all, by GFO.


Figure 5. Chelated (complexed) copper is very weakly removed by GFO, if at all.


Since iron is a major component of GFO, and this substance is subject to weak grinding action within a fluidized reactor, it might be expected that the iron content of the aquarium water would increase, and indeed it did. Further analyses found the iron to be almost entirely in the ferric form, but perhaps more importantly, as mostly in the form of suspended particulates and not dissolved. See Figures 6 through 9.


Figure 6. Experiment #1 showed total iron initially rose and then fell.


Figure 7. Results of experiment #2 found total iron concentrations rose and fell very much like that seen in experiment #1.


Figure 8. Total iron minus ferrous iron equals ferric iron.


Figure 9. Very little of the total iron was soluble but instead found in the suspended form.


Manganese is an essential element for plants and animals. Free manganese is actively removed by GFO, although the concentration of manganese in the spiked sample plateaued at ~0.07 mg/L at about 120 hours and thereafter. See Figure 10.


Figure 10. Manganese was actively removed by GFO. The analytical procedure can report Mn concentrations of 0.006-0.7 mg/L, while natural seawater contains ~0.001 to 0.01 mg/L.


GFO is advertised to effectively remove silica, and testing confirms this. Silica is quickly and effectively reduced in concentration, as its concentration fell to below the detection limit of the testing device (in essence 'zero'). See Figure 11.


Figure 11. Silica concentrations fell to below the detection limit of the instrument (essentially zero) inn less than 24 hours under the conditions of this experiment.


Zinc (free and not complexed) is rapidly removed by GFO. At 104 hours, the concentration had fallen from ~6mg/L to 0.38 mg/L (a removal of ~94%). See Figure 12.


Figure 12. The Detection Limit of the analytical device is 0.02 mg/L as Zn.


pH (the intensity of the basic or acidic natural of a substance) is known to be influenced through use of GFO. Figure 13 demonstrates this effect.


Figure 13. Use of GFO can cause rapid shifts in pH.


As with many elements, phosphorus is essential for life but can cause problems - specifically that of enhanced algal growths - at relatively low concentrations. Hobbyists should be concerned with reactive or ortho-, phosphate as this is the form that fuels algae growth (this is the form most all 'test kits' report). On the other hand, total phosphorus is that bound with other substances and requires a specialized digestion process including heat and an acidic environment. See Figures 14 and 15.


Figure 14. Time-course Total and Reactive Phosphorus concentrations. Reactive P fell to below the detection limit of the instrument (essentially zero) after only 12 hours. When we subtract…


Figure 15. …reactive phosphorus from total phosphorus, we find total phosphorus concentrations remain static. Total phosphorus is weakly, if at all, removed by GFO. This form of phosphorus is likely organically bound in suspended particles.

Reduction-Oxidation Potential (Redox) or Oxidation-Reduction Potential (ORP)

Redox, or ORP, is the tendency of an aqueous solution to gain or lose electrons from the introduction of a new substance. Redox measurements of a few natural reefs here in Hawaii are not substantially different than those taken during this procedure (See Figure 16).


Figure 16. At the first use of GFO, the redox value of the water trended upwards (the procedure began at 12:39 pm).

Trace Elements Addition

Addition of various metals to an aquarium can result from a number of factors ranging from inadvertent to deliberate. However, two likely account for most input: Feeding and water top-off and/or water changes. We'll examine these in some detail:

Fish Food: Many hobbyists, if asked, might say they do not deliberately add copper to their reef aquaria. The truth is that they do in the form of fish food. Prepared fish foods often contain trace amounts of copper sulfate, ferrous sulfate, manganese sulfate, zinc sulfate and potassium iodide.

Tap Water: Tap water may be from surface water (rivers, lakes), ground water (wells) and in some cases catchment (captured rain). Water quality varies with location, and elevated levels of nitrate, lead, copper, iron, manganese, calcium, magnesium and others may require pretreatment before release from the water treatment facility. In many parts of the country, water receives little treatment before distribution to customers, with disinfection (via chlorination, fluoridation or ozonation) being common. Small and private water systems are not regulated by the EPA, although guidelines have been established. Larger water systems are required to provide annual Consumer Confidence Reports (CCRs) that state levels of contamination if present. Bear in mind that clean water does not like to stay that way and often picks up contaminants from the plumbing within your dwelling.

Reverse Osmosis (or nano-filtration): Reverse osmosis is a popular means used to remove contaminants from water. Removal efficiency depends upon many parameters including type of pretreatment used and the type of reverse osmosis membrane used. In most all cases, removal of contaminants by RO filtration is not complete and small percentages of contaminants found in feed water are not removed.

De-ionized (DI) Water: DI water is often the most pure of waters regularly added to an aquarium either as that used to mix artificial salts or as top-off water. Functioning cationic/anionic de-ionization units can delivery water suitable for making dilutions when testing for various substances. Conductivity of DI water is low - mine produces water of just 4 or 5μS.cm2 Obviously, DI units can import little metals.

Well Water: Well water is naturally enough groundwater and is subject to absorbing any number of inorganic and organic substances in the soil. Private or small water systems using well water are not regulated by the US EPA and it is up to the owner(s) to determine suitability of this source for drinking or any other use for that matter.

Impurities in Supplements: We tend to think of the supplements added to our aquaria as being relatively pure when I fact they are not. For instance, 'laboratory grade' manganese chloride (ACS, 99.5% purity) contains 0.001% zinc and iron at 1.7 ppm. Technical-grade chemicals may be around 95% pure.

Natural Chelators: Aquatic humic substances are generally those produced by aquatic plants and algae either by biochemical pathways or through their decay. These substances can combine with metals in solution and cloak them from detection with most test kits used by hobbyists.

Artificial Chelators: Artificial chelators such as EDTA or EGTA can bond with metals. One major artificial seawater -Instant Ocean - advertises to contain no EDTA or any other metal chelators (see for details).

Water Motion, Boundary Layer, and 'Trace Elements'

All benthic objects are surrounded by a thin layer of stagnant water called the boundary layer. Its thickness is determined by the amount of water motion around the object, and is inversely proportional. In other words, the layer of stagnant water decreases when flow increases, and vice versa. Diffusion of elements through the boundary layer is related to the concentration of the substance in solution - the higher the concentration, the less likely it is to be limited by diffusion rates. The carry-home message is clear - insufficient water motion within a coral reef aquarium is to be avoided and directly affects the availability of 'trace elements.' Most aquaria do not even come close to 'natural' water motion where, in my experiences, sensors mounted to 5-pound lead weights can be tossed about by passing waves in even sheltered coves.

Metals in Natural Seawater

A water sample was collected in the littoral zone at the 4 Mile Marker on Alii Drive in Kailua-Kona, Big Island of Hawaii. This island is geologically young and metals bound in lava rock are leached by acid rain (a mixture of volcanic 'vog' -volcanic smoke containing tons of sulfur dioxide- and water vapor). The amount of copper found in natural seawater is roughly equivalent to that reported in the County of Hawaii drinking (ground) water Consumer Confidence Report (see Figure 17). This report does not include concentrations of iron and zinc.


Figure 17. Concentrations of copper and iron at the 4 Mile Reef in Kailua-Kona, Hawaii. There is likely a terregenous impact from acid rain leaching through geologically-young lava rock.


A brief review of existing journal literature leaves little doubt that at least some metals can be effectively removed by GFO.

The goal of this project was to establish metals removal/addition by iron oxide hydroxide. As with most endeavors of this type, results ask further questions. Metals concentrations within waters of captive environments are dynamic and subject to a number of influences such as pH, ionic strength or amount and type of chelators available. Even then, extraneous factors, such as poor water motion may limit the rate of metals' diffusion through a boundary layer. Whatever the case, supply and demand are ultimate factors.

GFO (at least the brand tested) has a high affinity for phosphorus and silica and rapidly removes ortho-phosphate and silicates. Copper in the free form is removed, while ferric iron is added, though in a particulate and not soluble form. Zinc, manganese, and cobalt are also removed though concentrations never fell to critical concentrations. It is possible that the testing process reported weakly-chelated metals.

Introduction of any chemical filtration could introduce competing processes in an aquarium, where the biochemical demand of animals competes with chemical extraction. No evidence was found where any element fell to critical levels. However, their initial concentrations were quite high and the salt content of water was only a fraction of natural seawater in the case of cobalt and manganese. Further simple colorimetric testing will likely lend little new useful data. More refined testing techniques will be needed before the impact of chemical filtration and its effects on metals is understood.

Methods and Materials

A 20-gallon aquarium was filled with seasoned artificial seawater (from a water change). Baseline measurements were made for reactive phosphate, iron, copper, zinc, and pH. The water was then spiked with copper chloride (Certified ACS) and 99% zinc sulfate (both chelated with EDTA, though apparently not enough as some free copper was determined through testing). Coarse bubble aeration was provided by a small air pump. The aquarium was not lighted, and incident light was only that from another aquarium approximately 10 feet away.

A different protocol was established in order to conduct testing for cobalt, nickel and manganese. These tests report erroneous results when magnesium concentrations exceed 300 to 400 mg/L Mg (as CaCO3). Additionally, the cobalt test is interfered by chloride (>8,000 mg/L), manganese (>25 mg/L) and sodium (>5,000 mg/L). To avoid these interferences, seasoned aquarium water was diluted with water previously treated via reverse osmosis. This water was then spiked with manganese (manganous) chloride (ACS grade; 99.5% purity) and cobalt chloride (ACS; 98.6% purity and chelated with EDTA). Baseline data were established for salinity, pH, iron, cobalt, manganese, magnesium, calcium, and alkalinity. Circulation within the tank was provided by a small powerhead (MaxiJet 400), and, as with the previous test, the aquarium was only weakly illuminated.

A sample of water was tested for total iron, and an aliquot of this sample was also filtered under vacuum through a 0.45 micron filter in order to determine if iron added to the aquarium water column is dissolved or particulate.

For each procedure, a fluidized bed reactor (Two Little Fishies) was filled with 60g (dry weight) Aquamaxx Phosphate Out GFO. A small water pump (Maxi-Jet 400) provided flow to the reactor which was regulated with a small ball valve to ~700 ml/min. The GFO was flushed with about 2 gallons of water before use and the reactor's effluent appeared clear to the eye. The reactor was installed on the experiment's aquarium and testing began. During testing for copper and zinc removal, new GFO (rinsed 60g dry material) was added after 8 hours due to a suspected saturation of the initial material (which was discarded).

Most test reagents were from Hach, and results were generated through use of a colorimeter (Hach DR890) or a spectrophotometer (Hach DR2000). Glassware was cleaned with 1:1 HCL (glassware used for manganese was cleaned with nitric acid) and rinsed with deionized water. Samples were drawn directly from the aquarium with cuvettes. Zinc samples initially required dilution; de-ionized water was used.

Quality assurance was conducted using a standard (Hach potable water standard). Recovery was >98% for both iron and copper and 93% for manganese.

Copper, iron, manganese, and zinc were analyzed by a Hach DR890 colorimeter. Cobalt and nickel were tested by a Hach DR2000 spectrophotometer. Alkalinity was determined with a Hanna Alkalinity 'Checker'. Salinity was measured through use of a calibrated refractometer. Silica was measured with a LaMotte Smart2 colorimeter. Redox (or oxidation-reduction potential) and pH were measured and recorded with a Hach HQ40d data-logger with appropriate probes. Reactive and total phosphorus (involving digestion) used Hach's TnT reagents and a block heater with analyses performed with a Hach DR2800 spectrophotometer.

These Hach reagents were used for testing:

Alkalinity was determined by titration of a sample with an acid of known strength to a standardized endpoint. This method is not the most reliable for testing of seawater. However, we are not concerned with absolute values and are more interested in relative alkalinity in order to demonstrate GFO's impact.

Cobalt (PAN Method; Range: 0.01 - 2.00 mg/L). Cobalt and nickel can be determined on the same sample using the PAN chemistry. Normal strength seawater must be diluted in order to properly perform this test - see 'Nickel' below for details. Determination is made at 620nm. A vigorous digestion was performed to determine total cobalt.

Copper (Bicinchoninate Method; Range: 0.04 - 5.00 mg/L). Since copper was complexed with EDTA, free copper was initially determined. Hydrosulfite was added to the same sample for determination of total copper. Estimated Detection Limit is 0.02 mg/L as Cu. No known interferences were present. No digestion was performed. EPA approved method.

Iron (FerroVer Method; Range: 0.03 - 3.00 mg/L). This reagent reacts with all soluble and most insoluble forms of iron (Fe2+ and Fe3+ as well as complexed iron) to produce soluble ferrous iron. 1,10-phenanthroline reacts with ferrous iron to produce an orange color. Estimated detection limit is 0.03 mg/L as Fe. No known interferences were present. No digestion was performed. EPA approved method. Other methods exist (using Hach's brand names):

Ferrous Iron Reagent tests for ferrous (Fe2+) iron only. 1,10-phenanthroline reacts with ferrous iron to produce an orange color. Since ferrous iron can be rapidly converted to ferric iron, samples must be analyzed immediately. Total iron - ferrous iron = ferric iron.

Manganese (PAN Method; Range: 0.006 - 0.700 mg/L). Ascorbic acid reduces all oxidized forms of Mn to Mn2+. An alkaline-cyanide reagent masks most interference. The PAN reagent (1-(2-Pyridylazo)-2-Naphthol) combines with Mn2+ to produce an orange color, which is measured with a spectrometer at 560nm. Magnesium interferes at a concentration of 300 mg/L (as CaCO3), so seawater samples must be diluted. Total manganese was determined on samples subjected to an EPA-approved vigorous digestion method.

Nickel (PAN Method; Range: 0.006 - 1.000 mg/L). Analysis involves the PAN method, where the sample is buffered and any ferric iron is masked by pyrophosphate, nickel and many other metals react with 1-(2-Pyridylazo)-2-Naphthol (PAN). EDTA is added to preferentially destroy metal-PAN complexes except for nickel and cobalt. Seawater samples must be diluted since they contain many interfering elements, such as chloride (8,000 mg/l), potassium (500 mg/l), magnesium (400 mg/l) and sodium (5,000 mg/l). Spectrometric determination is made at 560nm.

Phosphorus, ortho- or reactive (PhosVer3 Method). The estimated detection limit is 0.07 mg/L as PO 4 3- .No known interferences were present. EPA accepted method if no dilution is required. The aquarium water was tested before the procedure began - the result was 0.01 mg/l as P.

pH. This parameter was monitored and recorded with a Hach HQ40d multimeter/datalogger and pH probe. The meter was calibrated to two points - 7 and 10 pH buffers were used.

Silica (Heteropoly Blue Method). Reactive silica reacts with ammonium molybdate in acidic conditions to produce a yellow-green color. Since phosphate also reacts with molybdate, oxalic acid is added to prevent the interference. Silica-molybdate is then reduced by ascorbic acid to produce a blue color that can be measured through spectroscopy. These reagents were manufactured by LaMotte Company.

Zinc (Zincon Method; Range: 0.02 - 3.00 mg/L). This test is not listed as applicable to natural seawater since the expected concentration would fall well below the instrument's detection limit (0.02 mg/L as Zn); however no interferences prevent its use for determination of zinc at high concentrations in brine samples. Copper and iron concentrations fell below the levels known to cause interference. Zinc (and other metals) are complexed with cyanide (hence my obsession with sample pH) and cyclohexane selectively releases zinc. The Zincon reagent (2-carboxy-2'-hydroxy-5'-sulfoforamazyl benzene) reacts with zinc to form coloration ranging from orange to blue depending upon concentration. EPA approved method. No digestion was performed. EPA approved method.


Many thanks to Randy Holmes-Farley for his comments during the preparation of this article.


  1. Kanungo, S., 1994. Adsorption of cations on hydrous oxides of iron. II. Adsorption of Mn, Co, Ni, and Zn onto amorphous FeOOH from simple electrolyte solutions as well as from a complex electrolyte solution resembling seawater in major ion content. Journal of Colloid and Interface Science, 162(1), 93-102.
  2. Kanungo, S., 1994. Adsorption of cations on hydrous oxides of iron. III. Adsorption of Mn, Co, Ni, and Zn of bFeOOH from simple electrolyte solutions as well as from a complex electrolyte solution resembling seawater in major ion content. Reg. Res. Lab., Bhubaneswar, India. Journal of Colloid and Interface Science, 162(1), 103-109.
  3. Johnson, C., 1986. The regulation of trace element concentrations in river and estuarine waters contaminated with acid mine drainage: The adsorption of copper and zinc on amorphous iron oxyhydroxides. R. Sch. Mines, Imp. Coll., London, UK. Geochimica et Cosmochimica Acta, 50(11), 2433-8.

No publisher Dana Riddle Pomacanthus Publications, Inc. Chemistry And The Aquarium Chemistry and the Aquarium Dana Riddle GFO Chemistry Granular Ferric Oxide 2012-02-15T15:00:00Z Page
Aquarium Chemistry: Calcite, Aragonite, Limestone, and More It's been said a million times that aragonite helps buffer aquarium water, or helps maintain calcium concentrations, while other (carbonate) substrates do not. However, to the best of my knowledge this simply isn't true. Click through to see the images.


With the exception of something like an aquarium set up for jellyfishes, essentially all marine aquariums contain solid materials made of the minerals calcite and aragonite. Oddly enough, these two minerals are made of the same thing though, as both are composed of calcium carbonate in different forms. So, anything made of either or both of these are collectively known as carbonate materials, and I'm going to give you some information about each of these materials and a few other things, and explain what's what and how they're related to each other. That might not sound too exciting, but I'm sure you'll find this interesting and learn something good, nonetheless.


Essentially everything solid in our aquariums that isn't made of tissue is made of calcium carbonate, so it's worthwhile to know a bit about it.

Carbonate Minerals

Through the never-ending processes of weathering and erosion, rain and flowing water manage to slowly wear away various types of rocks and transport most of the sediments and dissolved substances produced in the process to the seas. Mixed in these rocks we can find dozens of elements, one of them being calcium. Thus, in the process of breaking down rocks, literally ton upon ton of calcium is washed into the world's oceans every year by streams and rivers.

On the other hand, in the atmosphere we find carbon dioxide, which is produced by animals as a respiratory waste product and the burning of organic matter, and exhaled by the Earth through volcanic activity. Carbon dioxide is also found in seawater, as it is given of by fishes and other animals and naturally dissolves into the water from the atmosphere, too. The process of diffusion allows it to constantly soak into surface waters exposed to air, after which it's mixed into deeper waters by the constant activity of waves and currents.

Then, under the right conditions, calcium, carbon dioxide, and water can chemically interact to form calcium carbonate - CaCO3. A number of other elements can end up in the mix, and can form some closely related compounds, as well. So, we tend to group all of these similar products together and call them the carbonates. Of these, the ones that are best related to the aquarium hobby are calcite, aragonite, and dolomite, which are the constituents of limestone (and thus live rock), carbonate sands and gravels, and the shells, skeletons, and other hard parts of various invertebrate organisms. So, let's take a look at all three of these minerals.


Calcite is a mineral that in its purest form is made of nothing but calcium carbonate. It is common in the marine realm and in rocks formed in marine waters, and it is chemically stable enough to resist being dissolved under common conditions. However, it oftentimes isn't so pure, as a few other elements commonly get mixed in during its formation. Some of these elements are magnesium, manganese, and iron, all of which have chemical properties that allow their incorporation.

So, as calcite is being formed, any of these elements present in the water that the mineral is being precipitated from can slip in from time to time and take the place of a calcium atom. Magnesium is the most common impurity of the bunch, so calcite is oftentimes called either low-magnesium calcite (LMC) or high-magnesium calcite (HMC) depending on how much magnesium is present in a given sample.


Like calcite, the mineral aragonite in its purest form is also made of just calcium carbonate. However, when aragonite forms the calcium, carbon, and oxygen atoms bond together differently and become arranged in a different pattern. The atoms in a sample of calcite are arranged in what's called a rhombohedral crystal, while the atoms in a sample of aragonite are arranged in an orthorhombic crystal.

Two different crystal forms made of the same stuff may sound odd, but it really isn't. This ability to exist in two crystal forms is called polymorphism, meaning many shapes, and I guarantee you've seen it before. Think about graphite, commonly known as pencil lead, and diamond. Graphite is actually one of the softest minerals, coming in at #1 on the Mohs Hardness Scale, while diamond is the hardest mineral known to man at #10, yet they're both made of exactly the same thing - carbon. Yep, both are made of nothing but carbon atoms which are simply found in different arrangements.

Calcite and aragonite certainly aren't as different as graphite and diamond, as they both have a similar hardness and are typically white in color. However, the change in atomic arrangements does change the list of impurities that can be easily included in aragonite. While calcite is commonly riddled with magnesium atoms, aragonite is typically found to be riddled with strontium atoms instead. Elements like barium and lead and a few others are also mixed in at times, but strontium is the most common of the bunch.

The structure of aragonite is also less stable than that of calcite, so it's more apt to dissolve under similar conditions. And, when strontium is added into the mix it becomes even more unstable. In fact, aragonite is considered to be a metastable mineral that can ever so slowly degrade to calcite all by itself over time at normal temperatures and pressures, without the help of water, with this change occurring even faster at high temperatures.


The third carbonate mineral to mention is dolomite, which is something like calcite with a very high concentration of magnesium in it. I'd said that calcite is typically riddled with magnesium atoms, but even in high-magnesium calcite the magnesium only makes up a small fraction of the whole. However, under some conditions there can be much more magnesium added in, and when the amount of magnesium becomes roughly the same as the calcium, the resulting mineral is called dolomite. So, dolomite is similar to calcite and still has a rhombohedral form, but it's chemical formula is CaMg(CO3)2.

Materials Composed of Carbonates

Now that you've got a basic idea of what carbonate minerals are, let's look at things that go into our aquariums that are composed of them.

Shells, skeletons, and other hard parts

Many organisms can extract calcium and other elements from seawater and then use carbon dioxide from the water or from their own respiration to precipitate carbonate hard parts. So, I'll run through some of the major users and the mineral(s) each uses:

Long ago there were some stony corals called rugosans and other called tabulates that are thought to have used calcite to form their skeletons. But, all of these disappeared from the Earth during the extraordinary Permian-Triassic mass extinction that occurred around 250 million years ago. Regardless, all of the stony corals that are with us today use aragonite to build their skeletons. However, almost all of the things that we lump under the name "soft coral" use calcite to form the tiny sclerites and spicules that support and strengthen their bodies.


Unlike modern stony corals, the extinct rugose corals used calcite to build their skeletons.

Likewise, all of the echinoderms, including the sea stars, brittle stars, crinoids, sea urchins, etc., use calcite to form the pieces, plates, and spines that make up their skeletons. All of the sponges belonging to the Class Calcispongiae use calcite to form their spicules. All of the hard tube-building worms, like Christmas tree worms, use calcite and/or aragonite to form their tubes. Some arthropods, like barnacles, use calcite to form the plates that make up their houses, while others may use calcite crystals to strengthen their protein-based shells. Most molluscs use aragonite to build their shells, although some clams and snails may use a combination of calcite and aragonite in layers, and a few others, like oysters, use calcite exclusively.


Carbonate sediments are oftentimes comprised primarily of bits and pieces of broken up coral skeleton, clam and snail shells, echinoderm parts such as sand dollar and sea urchin spines and tests, and other things like these bits of calcite that are freed to the environment when sea stars die.

Green calcareous algae, like Halimeda, also use aragonite to build their leaf-like blades, while, red calcareous algae, commonly called coralline algae, use calcite to form crusts and rinds over surfaces. And lastly, a wide range of plankton, like foraminiferans and coccolithophorids, use aragonite or calcite to build their tiny shells, as well.


Animals aren't the only things that use calcium carbonate. Various types of calcareous and coralline algae and several types of plankton do, as well. When these die, their hard parts also become carbonate sediments that are incorporated with those produced by animals.

So, as you can see, lots of invertebrates use calcium carbonate to make their hard parts (while vertebrates use calcium phosphate to make theirs). However, as you may have also noticed, dolomite is not used by any marine organisms to produce hard parts. For that matter, geochemists haven't even figured out how to make it themselves in a lab under conditions that can be found in the marine environment. How it forms in different geological settings has been argued for years, and the jury is still out on exactly how the transition from magnesian calcite to dolomite occurs, but what I can tell you is that it isn't forming in significant quantities in any of the modern marine environments, with or without the help of organisms.

Aragonite and oolite sands

Most of us have some fine sand in our aquariums, and the most commonly used type is aragonitic sand. So, it's composed of bits of aragonite with varying origins. Some of the aragonite sands available are relatively coarse and are made of ground up sea shells, while others are very fine with the grains primarily being smaller bits of various organisms' hard parts produced when wave activity and bioeroders like parrotfishes break down their shells and carbonate rocks, etc. However, there are some other products called oolitic sands that look pretty much like any other fine sand, but are actually quite different in origin.


Animals like parrotfishes and sea urchins are considered to be bioeroders, as they're organisms that chew on various rocks and substrates and produce sediments in the process. Parrots bite off pieces of limestone and ingest them, digest whatever was living on them, and then defecate copious quantities of carbonate sand later. Likewise, many urchins use their hard "teeth" to grind coralline algae off rocks, and also produce carbonate sand in the process.

Oolitic sands have normal-looking white to pinkish-white grains, but they're composed of tiny structures that are not derived from organisms' hard parts. Almost all modern ooids are indeed composed of aragonite, but some are HMC, and some are composed of both. To the contrary, almost all ancient ooids, which is what many oolitic sands being sold are comprised of, are calcitic. Regardless, they all look like tiny bites of hard candy when cut open. They may be smooth and shiny on the outside, but the inside can have numerous layers and coatings, or tiny fibrous crystals, and again, none are produced as hard parts by organisms. Instead, while the details aren't well-understood, these are produced abiotically in various marine environments.

Shelly substrates

There are many other substrates available that are comprised of small sea shells, or larger pieces of ground up shells. Examples are the "puka" substrates and crushed oyster shell. Since most molluscs use aragonite to build their shells, most puka gravels will of course be composed of aragonite. However, as I mentioned above, oysters are an exception to the general rule and make their shells entirely of calcite. So, crushed oyster shell gravel is composed of calcite.


Some substrates are comprised of small but whole shells, and are thus composed primarily of aragonite.

Crushed coral gravels

In light of the fact that stony corals use aragonite to build their skeletons, it should make perfect sense that any bags of gravel labeled "crushed coral" are in fact bags of aragonite. However, I've also seen many bags of crushed coral gravel that were actually bags of dolomite (it said so right on the bags). This is odd because dolomite isn't collected from modern reef environments, and it certainly isn't ground up coral or hard parts of any other organisms, either.

I suppose it's possible that this particular kind of gravel could be produced from some rock formation containing fossilized corals that were buried, turned into dolomite over millions of years, then dug up and ground into gravel. But, I can assure you that it isn't collected around modern reef environments and isn't made by crunching up the skeletons of dead non-fossil corals, either. Does that mean there's anything wrong with using it? Well, like puka or crushed oyster shell gravels, it's really not a good size for a reef aquarium substrate since it tends to get completely clogged with detritus when there's no significant water movement through it, but I probably used about a ton of it setting up tanks with undergravel filters in the past since it was white in color and exactly the right grain size for the job.

Limestone and live rock

At this point I'm sure you can understand that the vast majority of carbonate sediments found in reef environments are actually chunks and bits of various organisms' hard parts including eroded coral skeleton and snail and clam shells, etc. with a large amount of broken up calcareous algae thrown in, too. Now let's get to how rocks can be made from these.

When all of these carbonate sediments are deposited together around reefs and slowly compacted by the constant addition of more sediment, additional carbonate material can abiotically precipitate from seawater in the miniscule void spaces between the sediments and cement them together. So, under the right environmental conditions sediments can literally get glued together by even more calcium carbonate. Then, after enough time and under the right conditions, the sediments and cements themselves can be dissolved to some degree, followed by more abiotic precipitation too, which is how most live rock and much limestone come to be. In fact, live rock really is limestone, although there are other types of limestone that can form through a variety of abiotic processes.


Here you can see a mess of carbonate materials that are weakly cemented together. While not quite limestone, this material was certainly on its way to becoming solid rock before being exposed.


Given enough time, materials like these pieces of Acropora palmata and A. cervicornis can be buried along with carbonate sand and other bits of stuff, glued together by carbonate cements, and eventually turned to solid limestone as seen here.

Regardless, while live rock and limestone are obviously composed of calcium carbonate, oftentimes there are no distinct grains or pieces left in either that you can pick out. Want a good example? Just cut or break a piece of live rock in half and take a good look. You'll likely find the blurred remnants of coral skeletons and other things all cemented together and transformed from carbonate sediments into stone. So, as you can see, most everything that we call sand, gravel, rock, etc. that comes from reef environments is actually made up of carbonate material produced by the organisms right there on the reef.


Busting a piece of live rock open will typically reveal some remnants of the coral skeleton, shell material, etc. that were originally un-cemented sediments.

Wrap up

Okay, so I imagine that at this point you might be wondering if there's any good reason to pick things that are made of aragonite over things made of calcite, or vice versa. It's been said a million times that aragonite helps buffer aquarium water, or helps maintain calcium concentrations, while other (carbonate) substrates do not. However, to the best of my knowledge this simply isn't true.

I have yet to see any solid evidence that using aragonitic materials provides any advantage over using calcitic materials in an aquarium. And, in the words of the chemist-aquarist-author Randy Holmes-Farley "calcium carbonate will not dissolve in the water column of normal marine aquaria". Some may dissolve within a deep sand bed where water chemistry changes from the top of the bed to the bottom, but this is unlikely to have any significant effect on overall water quality. So, I wouldn't waste a minute of my time worrying about whether or not something is made of one or the other, or of dolomite either for that matter. Still, I hope this has helped you to understand the carbonates and many of the terms we see that are associated with them, and why calcium additions to reef aquariums are so important, too.

References and sources for more information

  1. Aragonite:
  2. Bioerosion:
  3. Calcite:
  4. Coccolithophorids:
  5. Dolomite:
  6. Foraminiferans:
  7. Holmes-Farley, R. 2002. Chemistry and the Aquarium: Calcium Carbonate as a Supplement. Advanced Aquarist, 1(7).
  8. Limestone:
  9. Ooids:
  10. Ooids:
  11. Rugose corals:
  12. Permian-Triassic mass extinction:
  13. Tabulate corals:

No publisher James W. Fatherree Pomacanthus Publications, Inc. James W. Fatherree Aquarium Chemistry Dolomite Calcite Aragonite 2011-10-26T12:00:00Z Page
AmericanReef Video Podcast: Part II - Can Coral Reefs Survive Ocean Acidification and Global Warming? American Reef returns to Reef Systems Coral Farms, a collaborator in an important study of how both global warming and increasing ocean acidity affect coral life. Part 2 of 2. Click through to see the images.

Researchers from Ohio State University, the University of Delaware, and the University of Georgia plan to identify corals resilient to these stressful conditions, as well as pinpoint factors that could fortify resiliency. Known as the 4Coral Research Group, these scientists hope the results of their experiment can be used by conservationists to focus their preservation efforts. As always, send any questions to or sound off in the comments below.

Watch The Video...

No publisher Russ Kikel Pomacanthus Publications, Inc. temperature Aquariums Russ Kikel Water Quality Article Podcast 2011-09-29T12:00:00Z Page
Product Review: Inexpensive Analytical Devices: Hanna Instruments' Checkers: Alkalinity and Phosphate In many cases, results from colorimeters are superior to visually judging colored samples. Will an inexpensive device deliver results comparable to an expensive spectrophotometer? Dana tests the Hanna Checkers to find out. Click through to see the images.


When I first started work in a laboratory, determination of various aqueous constituents was a laborious task, beginning with mixing standards, manually graphing their absorbances, and then making comparisons with samples' absorbance tests results. We manually recorded this information and charted it on graph paper. It was state-of-the-art for the 1970's. We would be (and are) amazed with today's analytical instruments. Compact, battery-operated colorimeters (a type of spectrometer) use conveniently packaged chemicals to quickly determine concentrations of various aqueous substances.


Of particular interest to me in this new world of laboratory instruments are devices used to analyze for alkalinity and phosphorus. Hanna Instruments offers relatively inexpensive colorimeters called 'Checkers' priced at about $50-$60 each (including a small supply of reagents, 2 test tubes, and carrying case). These instruments are small and highly portable. But how accurate are they, and are they worthy of your consideration? This article will attempt to answer these questions.

Hanna Instruments


Why Test?

Since you're reading an article about testing for phosphorus and alkalinity, I'll make an assumption you understand the role they play in aquaria. If you'd like to learn more about these, see:

  1. Phosphates:
  2. Alkalinity:


The following terms are used in this article:

A vessel for holding water, especially a transparent laboratory vessel (such as a test tube)
A device for determining the concentration of a substance dissolved in liquid by comparing the intensity of its color with that of standard solution(s) of known concentration(s)
milligrams per liter, essentially the same thing as ppm
parts per million
A substance for use in a chemical reaction, especially for analysis
For our purposes, an optical instrument capable of measuring intensity of transmitted light at a specific (but varying) wavelength, especially for determining the concentration of a dissolved substance
The liquid reagent used in titrations
A method for determining the concentration of an aqueous substance by adding a liquid reagent of known concentration and measuring the volume necessary to convert the substance from one form to another

Methods and Materials

First of all, the results shown here are simply comparisons of those gathered by different analytical means. No standards were tested, and I am operating on the assumption that results of Hach's EPA-approved methods and a 'laboratory-grade' spectrometer are most accurate. In addition, only one Hanna instrument each was used in these comparisons.

Water, gathered from a functioning marine fish-only aquarium, was used for the testing.

Samples tested for phosphate were gathered in acid-washed glassware and analyzed within a few hours' time. Initial analyses indicated the phosphate content was at the upper detection limits of both instruments used (a Hach DR2800 spectrometer and the Hanna HI-713 colorimeter). Simple dilution with deionized water brought the phosphate to concentrations spanning the full range of both instruments and to levels realistically found in many reef aquaria. The Hanna and Hach devices both use the ascorbic acid chemistry method for analyses.

Comparing alkalinity results is not as straight-forward. The Hanna device estimates alkalinity through colorimetric analysis. Apparently Hanna has made correlation of chromatic shifts (indicating pH) and the impact of an acidic titrant on alkalinity. While making for a quick and convenient test, there are caveats. First, the amount of alkalinity determines the titration endpoint. In addition, the presence or absence of phosphate and/or silica also affects testing protocol (See Table 1 for titration endpoints).

Table 1. Titration end-point pH Values.
Test Condition End-Point pH Values
Alkalinity Concentration (as ppm CaCO3): 30 4.9
150 4.6
500 4.3
Silicates, Phosphates present or suspected 4.5

For comparative purposes, alkalinity values were determining using the Hanna's colorimetric method and an end-point pH titration method. Hach reagents (sulfuric acid, either 0.160 or 1.600N) were used to titrate a magnetically-stirred sample. A calibrated meter monitored pH.

End-points depended upon alkalinity values shown in Table 1 while Figure 1 shows various endpoints based on alkalinity concentrations. Figure 2 is a photo of equipment used in measuring alkalinity according to EPA guidelines.


Figure 1. Titration endpoints for determining alkalinity while using Hach reagents.


Figure 2. Measuring alkalinity according to EPA guidelines requires a bit of laboratory equipment.

With background information out of the way, we can now turn our attention to Hanna's HI-755 and HI-713 devices.

Alkalinity: Hanna Instrument HI-755

Hanna advertises these specifications for their Alkalinity Checker:

Hana Specifications for Alkalinity Checker
Item Specification
Range: 0 to 300 ppm (mg/L) (some retailer ads incorrectly say 250 ppm)
Resolution: 1 ppm (or mg/L, if you prefer)
Accuracy : ±5 ppm (mg/L) ±5% of reading @ 25°C (77°F)
Battery Type: One 1.5V AAA (included)
Light Source: LED @ 610 nm
Light Detector: Silicon photocell
Environment: 0 to 50°C (32 to 122°F); 95% Relative Humidity maximum, non-condensing
Auto-off: Yes, after ten minutes of non-use
Weight: 64 grams (2.25 oz.) - actually a little heavier (~75 g - yes, I checked!)
Colorimetric method, using a liquid pH indicator (bromcresol green)

As discussed in detail in the Methods and Materials section, the results from the Hanna Checker were compared to analyses performed by the acid titration method using endpoints dictated by alkalinity concentrations and the presence of phosphates and/or silica. The results are shown in Figure 3.


Figure 3. The Hanna Alkalinity Checker consistently reported values higher than those measured by the pH-endpoint titration method, but see Discussion (below).

Next, we'll look at the Hanna Phosphorus Checker. Hanna advertises these specifications:

Phosphorus (Low Range), Hanna Instrument HI-713

Suitable for freshwater, brackish and seawater. Model Tested: HI-713 Phosphorus, Low Range

Hana Specifications for Low Range Phosphorus
Item Specification
Range: 0.00 - 2.50 ppm (mg/l) as Phosphate (PO43-)
Resolution: 0.01 ppm (mg/l)
Accuracy : ±4 % of reading @ 25°C (77°F)
Battery Type: One 1.5V AAA (included)
Light Source: LED @ 610 nm
Light Detector: Silicon photocell
Environment: 0 to 50°C (32 to 122°F); Relative humidity: 95% maximum, non-condensing
Auto-off: After two minutes of non-use, and ten seconds after reading
Weight: 64 grams (2.25 oz.)
Analytical Chemistry: Ascorbic Acid Method: Ammonium molybdate and potassium antimonyl tartrate react in an acid medium with ortho-phosphate to form phosphomolybdic acid that is reduced to molybdenum blue by ascorbic acid.
Interferences: Silicates in excess of 10 mg/l; highly colored water (such as visibly yellow water)

As discussed in detail in the Methods and Materials section, the results from the Hanna Checker were compared to analyses reported by a Hach 2800 spectrometer and ascorbic acid reagent. The results are shown in Figure 4.


Figure 4. The results generated by the inexpensive Hanna Checker are remarkably close to those reported by a $3,500 spectrometer.

Comments and Recommendations

In many cases, results from colorimeters (and other photometric devices such as spectrometers) are superior to visually judging (comparing) colored samples. In fact, Standard method states: Visual comparisons of treated samples in Nessler tubes is not better than 5% (more often 10%) whereas photometric analyses can be reliable to within 3%, depending upon many factors. Naturally, the photometric device can eliminate personal biases of the user as well as accurately and precisely differentiate between small increments of sample absorbance/transmission.

If photometric analyses are potentially superior, the question of device engineering and quality becomes the issue (that is, will an inexpensive device deliver results comparable to an expensive one?). Under the conditions stated in the Methods and Materials section (above), these observations and recommendations are made:

Hanna Alkalinity Checker

These observations apply to the Hanna Checker HI-755 (Note the instrument is marked 'Checker Marine' suggesting it is intended for seawater analyses only):


  • Easy to use
  • Results are generated in seconds
  • The procedure is simple - no drip titration is required (just add reagent, shake, and read)
  • Does not require any manual conversions (results are expressed as parts per million calcium carbonate)
  • Replacement reagent is inexpensive
  • Auto-shutoff
  • Reagents marked with expiration date
  • Small sample size (10 milliliters)
  • Spare cuvette included
  • Directions and MSDS available online


  • Alkalinity measurements were consistently higher than those generated by the titration/pH end-point method
  • Multiple measurements are not possible without zeroing the instrument each time
  • No Material Safety Data Sheet included (see below for link)
  • Reagent will stain skin and clothing (all procedures using organic dyes carry the same risk)
  • Battery replacement requires a small screwdriver and removal of a tiny screw

Recommendation (Alkalinity):

Though my quick comparisons showed the Hanna Alkalinity Checker delivered results consistently higher than those obtained with an EPA-approved method, I am impressed with the speed and ease of measurement. If I were to establish a correction (and comfort) factor to apply to the Hanna Checker's results, this would be my method of choice for establishing alkalinity concentrations.

I recently received a Hach catalog advertising their version of a colorimetric alkalinity test. Hach's chemistry, just as Hanna's, apparently uses bromocresol green sodium salt in the analysis method. It seems this method is becoming widely accepted, if only for estimations (this is not an EPA-accepted procedure).

Recommendation: Yes, with some reservations


  • 1 ppm Alkalinity as CaCO3 = 0.02 milliequivalent per liter (meq/L)
  • 1 ppm Alkalinity as CaCO3 = 0.056 degrees Carbonate Hardness (dKH, or German Hardness)

Hanna Phosphate Checker

These observations apply to the Hanna Checker HI-713 (Low Range Phosphate):


  • Results compare very favorably with those generated by a much more expensive device
  • Much less expensive than a full-blown spectrometer or photometer
  • Easy to use and portable
  • Results are generated in several minutes (including a 3-minute reaction time)
  • The Checker incorporates a timer
  • The procedure is simple - Add reagent, shake and bake for several minutes, and read results in parts per million as phosphate
  • Replacement reagent is competitively priced
  • Auto-shutoff
  • Reagents work in fresh, brackish, and saltwater
  • Reagents marked with expiration date
  • Low Battery, Dead Battery, Under Range, Over Range, Inverted Cuvettes, High Light and Low Light errors are displayed when appropriate
  • Small sample size (10 milliliters)
  • Spare cuvette included
  • Directions (but not MSDS) available online


  • Test results for phosphate are displayed for only 10 seconds after they are reported
  • Multiple measurements are not possible without zeroing the instrument each time
  • No Material Safety Data Sheet available

Recommendation (Phosphate): Yes!

Footnote: To convert PO43 to P, divide by 3.066

Reagent Cost Comparisons

The following approximate prices are for replacement reagents only, and do not include instruments (unless noted), taxes, insurance, or shipping costs.


  • Hanna Phosphate Reagents: $27.99 U.S. per 100 tests
  • Hach PhosVer3: $28.19 U.S. per 100 tests (10 milliliter sample)
  • Footnote: The Hanna HI-714 phosphate colorimeter can use Hach reagents (ascorbic acid powder pillows).


  • Hanna Alkalinity: $9.99 U.S. for 25 tests (~40 cents per test)
  • Hach: Alkalinity for digital Titrator, $59.17 - includes sulfuric titration cartridges, phenolphthalein and bromcresol green/methyl red reagents. $219 includes reagents and Digital Titrator. To comply with EPA guidelines, a pH meter is also required, and a magnetic stirrer is useful.
  • Hach's new colorimetric Total Alkalinity test (25-4,000 mg/l as CaCO3): 25 tests for $31.45 ($1.26 U.S. per test) using only their spectrometer models DR2800, 3900 and 5000 (Note: These spectrometers begin at about $3,500 U.S.)

Material Safety Data Sheets (MSDS)

The two kits I obtained did not include Material Safety Data Sheets. Here is a link to the Alkalinity reagent: I could not find a link to the Low Range Phosphate reagents on Hanna's website at the time of this writing.

Sampling Procedures

"Garbage in; Garbage out" is a saying applicable to results generated when improper sampling procedures are in place. Use reasonable care when gathering samples for analyses. It is recommended that the vials (cuvettes) supplied by Hanna are used when sampling to avoid contamination.

Alkalinity: Analyze immediately or fix sample by refrigerating at 4°C (39.2°F) for up to 24 hours. Bring to room temperature before analysis. If the sample is gathered in a container other than Hanna's cuvette, either clean plastic or glass is OK, and it should be completely filled to avoid prolonged exposure to any air trapped in the bottle. Filter if the sample contains excessive suspended particles.

Phosphate: Analyze immediately. Use the Hanna 10 milliliter cuvette to draw the sample if possible. If not possible, use clean plastic or glass containers - they should be scrupulously clean - preferable acid-washed with 1:1 hydrochloric acid and rinsed with de-ionized water. To fix the sample, exclude particulate matter via filtration and refrigerate at 4°C (or 39.2°F). Maximum holding time is 48 hours.

Treat the cuvettes with respect, and keep them clean and free of scratches. Don't allow the treated samples to remain in the cuvettes any longer than necessary as the chemicals might stain the glass. If the vials do become stained, gently clean them with paper used for sensitive applications (such as that used to clean camera lenses). In extreme cases, a dilute bleach solution may be required to remove the stains. Some hobbyists keep the vials filled with deionized water between uses to prevent spotting within them.

Other Instruments from Hanna



Contact Information



Or write to:

Hanna Instruments, Inc.
584 Park East Drive
Woonsocket, RI 02895

Additional Comments

These products were obtained through normal retail channels, and descriptions, specifications and other information were current at the time of writing.

Questions? Comments? I am best reached at: or sound off in the comments below.


  1. Holmes-Farley, R., 2006. Phosphate and the reef aquarium.
  2. Holmes-Farley, R., 2002. Chemistry and the aquarium: Solving calcium and alkalinity problems.

No publisher Dana Riddle Pomacanthus Publications, Inc. Alkalinity Phosphates Water Testing Product Review Dana Riddle Water Quality Phosphate 2011-08-24T12:00:00Z Page
AmericanReef Video Podcast: Can Coral Reefs Survive Ocean Acidification and Global Warming? American Reef returns to Reef Systems Coral Farms, a collaborator in an important study of how both global warming and increasing ocean acidity affect coral life. Part 1 of 2. Click through to see the images.


Watch The Video...

No publisher Russ Kikel Pomacanthus Publications, Inc. temperature Aquariums Russ Kikel Water Quality Article Podcast 2011-08-17T12:00:00Z Page
Feature Article: Experimental Comparison of Measured Flow Output of Aquarium Propeller Pumps Hobbyists have seen significant advancements in the range of aquarium circulation pumps available over the past decade. While all manufacturers provide a flow rate for the pumps, it is not clear what methods have been used to arrive at the numbers. Further, different manufacturers may use different methods. We have presented a standard method that we hope can be adopted by the manufacturers thus enabling a more accurate and verifiable approach. Click through to see the images.

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The purpose of this study was to investigate a method to more accurately determine the output flows of several aquarium propeller pumps. To complete this investigation, a test setup was constructed in a 350 gallon aquarium tank using a Sontek 10-MHz Acoustic Doppler Velocimeter for data acquisition. The velocity profile of the pump exit flow was measured at a distance of one diameter downstream from the output of the pumps and used to determine the volume flow rate output. The results of this investigation reveals that there can be large variability between the manufacturer's advertised flow rates for propeller driven pumps and the flow rates measured by this method. The results suggest that a standardized approach to measuring flow should be created to better enable manufacturers to more accurately advertise the correct flow rates so that consumers can choose the appropriate pump for their aquarium.

Flow in the Aquarium

Sufficient water movement in aquariums is known to be an important component for animal health and long term success. In general, most reef hobbyist attempt to maximize the water movement within their aquarium (flow rate) using pumps, power heads, or wave devices while minimizing the maximum velocity of the water "hitting" sessile animals. This prevents shearing off of tissue and disturbing the health of corals. The flow rate is defined as the amount or volume of water moved per unit of time and is usually provided in units such as gallons per hour or liters per hour.

However there are no simple rules on how to adequately quantify the amount and type of water motion needed for aquarium success. Reasons for this include the lack of a detailed data and real understanding of the needed water movement or type of movement necessary for specific animals. In general, the amount of water motion for corals has been linked to the location of specimens relative to the reef zone (such as fore reef, reef flats, lagoon, etc). However in reality the water motion in the ocean is very chaotic both in short (seconds, minutes) and long (hours, days and longer) time scales. In an aquarium the amount of achievable flow at any point is further complicated and impacted by both aesthetic (non-living) and living (such as coral) structures, placement of pumps, and tank walls; all of which add friction, change flow direction and constrain or limit water movement. Also any structure in the path of water flow can induce change in flow directions, secondary flows, momentum losses, unsteadiness and turbulence.The aquarium industry characterizes the pumps using the flow rate - amount of water moved per unit of time (eg. Gallons/hr). However, the more accurate definition of volumetric flow rate is " the volume of fluid which passes through a given surface area per unit time" This definition indicates that there is a velocity component to the flow. For a fixed surface area, the volumetric flow rate can be increased or decreased by changing the flow velocity. Also, a fixed flow rate can be achieved by increasing the velocity and reducing the surface area or by decreasing the velocity and increasing the surface area.Given an area A, and a fluid flowing through it with uniform velocity V with an angle away from the perpendicular direction to A, the flow rate is:

Q = (V)(A) cos θ (1)

In the special case where the velocity is perpendicular to A,

Q = (V)(A) (2)

In general, the flow velocity at any location in the ocean (or in the aquarium) can be in any direction and can be defined by a vector or

equation3.png (3)

Since the direction and magnitude of the velocity may change in time, the water velocity can also be defined by

equation4.png (4)

where vectoris the mean velocity component of the fluid and V' is the unsteady or time-varying component . The magnitude and direction of the unsteady component, V'(t) is a function of time. The unsteady component can also be sub-classified as deterministic (such as periodic or coherent variations in water movement due to waves or wakes from the rotating propeller blades) or non-deterministic (random motion or turbulence). Turbulence is initiated by shear or gradients in flowing water and is characterized by chaotic mixing of the water through large scale eddies which spawn ever smaller scale eddies.

In the aquarium, water movement is typically achieved using powerheads or pump driven return pipes and closed loop circuits. The outlet portion of each of these devices results in the generation of a submerged jet similar to what is shown in Figure 1 for a simple submerged turbulent jet. Submerged jets are jets of water that flow into a reservoir (tank) of water. Contrary to common aquarium myth, in most cases, except possibly the smallest powerheads, the jet is turbulent and not laminar. Also, as will be shown in this paper, the exit flows from propeller driven pumps are much more complicated than a simple jet shown below.


Figure 1. Schematic of simple turbulent jet [1]


The use of propeller bladed pumps/powerheads for water movement in the aquarium industry has expanded significantly in the past few years with the advent of DIY, retrofit kits, and specific commercial lines. The first propeller pump available to reef aquarist consumers was created by Jimmy Chen in 2002 and sold as a retrofit kit to be installed on a Little Giant submersible pump [2]. While providing high flow rates with minimal power consumption, this product did not feature the benefit of long term research and development and was plagued by failures. Tunze unvieled the first widely available commercialized propeller pumps at Interzoo in May 2002 branded as the "Tunze Stream." The synchronous models of Stream were available at retail in July 2002 and the controllable models followed in November. They also offered brushless DC models which were capable of speed control through their own proprietary controller.

In 2005 EcoTech Marine introduced a through-the-glass magnetically coupled aquarium pump, using a brushless DC, controllable motor. More recently, Hydor introduced their Koralia line of propeller pumps and made available controllable versions as well. The Hydor line of controllable powerheads is distinctly different from the Tunze and EcoTech Marine products because it utilizes low voltage AC current to drive the pumps and the controllers use frequency modulation to change the speed. The major difference of these two approaches is that brushless DC pumps are typically more expensive but their controllers are relatively inexpensive, whereas low-voltage AC pumps are more economical however their controller is expensive to produce. Generally, brushless DC pumps are capable of more precise rpm changes to enable flow augmentations such as pulsing for waves generation.

The objective of the current experiment was to investigate a more accurate method to determine the volumetric flow rates for widely available models of propeller pumps. The advantage of propeller pumps is that they are capable of moving large volumes of water at very low pressures with minimal power consumption. Some DIY methods of measuring the flow rate of small pumps include timed bag filling experiments, pumping from one reservoir to another and placing the powerheads in a constrained systems (inlet or exit piped) with a flow meter. These types of tests however, can impart unrealistic hydrodynamic loads on the propeller pumps by altering the inlet and/or exit flows in ways that are not typically seen in our aquarium set ups. Adding piping and other constraints such as bags on the exit jet may impart back-pressure that can affect the pump's performance. These DIY methods add additional blockage (similar to covering the exit jet or inlet grating) which negatively reflects the true flowrate of the pump. In addition, the pump exit jet flow tends to expand radially as it exits the nozzle as shown in the Figure 1. Any intrusive method (such as a bag, added piping, increased pressure head between reservoirs) adds momentum and friction losses not accounted by most measurement methodologies. Therefore more sophisticated methods must be employed to obtain accurate flow readings from propeller driven pumps. An experimental method was developed incorporating acoustic Doppler velocimetry (ADV) technology, which has been used to measure open channel flow. The advantage of this methodology is that it is nearly non-intrusive and does not apply backpressure to the pump. It also measures the flow velocities directly in contrast to diffusion/dissolving methods which only infer flow rates [3].

The pumps included in this study are listed in Table 1 along with their manufacturer's advertised flowrate. Due to the expense of some of these products and constraints on the budget, every product on the market could not be included in this evaluation. The study was restricted to the following list of pumps shown in Table 1.

Table 1. Pumps included in flow experiment
Pump Advertised Output Flow (Gallons/hr)
Aqueon 2400 2400
Coralife CP 2900 2900
Ecotech Marine MP-10 1575
Ecotech Marine MP-40 3200
Ecotech Marine MP-60 7500
Hydor Koralia 5 1650
Hydor Koralia 6 2200
Hydor Koralia 7 2700
Hydor Koralia 8 3250
Maxijet 1200 295
Tunze 6105 3434
Tunze 6205 5811
Tunze 6305 7925

The majority of the pumps included in this test cater to the high-end saltwater aquarium market. A less expensive traditional impeller driven Maxijet 1200 powerhead was included in this test as a comparison to propeller pumps.


Because these propeller based aquarium pumps operate between two fluid reservoirs that are at the same pressure, one cannot simply displace water from one reservoir to another without adversely affecting the accuracy of the measured volume flow rate. For this reason, a velocity measurement of flow is needed to determine the true volume flow rate through the pump. A single velocity measurement is not sufficient for propeller pumps since the flow velocity varies across the large diameter cross section of the exit nozzle. To accurately measure the velocity of the flow across the entire output profile, several sample measurements were taken at locations ranging from the very outside of the flow jet to the center of the flow jet. For the purpose of this experiment, the flow was divided into n distinct regions, illustrated in Figure 2.


Figure 2. Division of flow based on radial position

After measuring the flow velocity in these regions, the subsequent volume flow rate of the region can be found using

VFRi = Vi*Ai (5)

where, VFRi is the volume of water flowing per unit time through the incremental area Ai at velocity Vi . This calculation can be repeated over the velocity profile to yield the total volume flow rate of the system. This idea can be expressed as

VFRs = Σ Vi * Ai. (6)

The area of each region can be calculated using

Ai = π * (ri2-r(i-1)2). (7)

This type of calculation is known as a Reimann Sum, and is used to approximate real-world integration. The accuracy of this method depends greatly on the number of iterations completed.

Experimental Apparatus

For this experiment, a test setup needed to be developed that would accurately measure the velocity of water flow over a series of points across the flow profile. To accomplish this task, a Sontek 10-MHz Acoustic Doppler Velocimeter was selected for its ability to measure open-channel flow in a volume of water as small as 0.25 cc. The ADV selected also had the capability of measuring 3-Dimensional flow. Table 2 is taken from Sontek's literature for the 10 MHz ADV used.

The ADV that was used to collect the velocity measurements was positioned using an extruded aluminum scaffolding system shown in Figure 3. The system was designed to be adjustable in the three dimensions shown, labeled X, Y, and Z. The vectors shown correspond to the ADV measurements taken for the X, Y, and Z directions.

To accurately measure the position of the ADV over the course of each trial, the scaffolding structure in Figure 3 was fitted with Wixey Model WR510 digital positioning gauges on both the Z and the Y axes. The specifications for the gauges used are shown in Table 3.

Table 2. Sontek Adv Specifications
Sontek 10 MHz ADV
Sampling Rate 0.1 to 25 Hz
Sampling Volume 0.25 cc
Distance to Sampling Volume 10 cm
Resolution 0.01 cm/s
Programmed Velocity Range 3, 10, 30, 100, 250 cm/s
Accuracy 1% of measured velocity, 0.25 cm/s
Maximum Depth 60 m
Temperature Sensor 0.1°C
Resolution - Heading,Pitch, Roll 0.1°
Accuracy - Heading ±2°
Accuracy - Pitch, Roll ±1°

Figure 3. Scaffolding support structure for ADV positioning

Table 3. Specifications for Wixley Model WR 510
Wixey Model WR 510
Resolution: Decimal = .005 in.
Fraction = 1/32 in.
Metric = 0.1 mm
Accuracy: Decimal = .0025 in.
Fraction = 1/500 in.
Metric = .05 mm

Figure 4 shows the setup of the positioning and integration of one of the gauges used. This test setup allowed for accurate recording of the position of the ADV to within 0.05 mm, as listed in the specifications. Because positioning in the X direction was less critical, a tape measure was used to position the ADV at approximately one diameter downstream from the face of the pump, +/- 1/32nd of an inch.


Figure 4. Integration of digital positioning gauges into scaffolding structure

Figure 5 shows the final ADV positioning for testing of the Tunze 6305. As shown in the figure, the ADV is positioned at the centerline of the pump face and one diameter downstream from the face.

Figure 5 also shows the particulate matter that was suspended in the tank for the duration of testing. These particulates were the seeding material provided by Sontek in order to increase the signal-to-noise ratio returned by the velocimeter.


Figure 5. Initial positioning of the ADV during testing

Besides the velocity components and standard deviation of the axial velocity, the power consumption and the rotational speed of each pump were recorded. The power consumption was monitored through a wattmeter which is shown in Figure 6. The rotational speed of each pump was determined using the strobe tachometer shown in Figure 7. Figure 8 shows the tachometer in use while testing the Coralife CP 2900.


Figure 6. Watt meter used in testing


Figure 7. Strobe tachometer used in testing


Figure 8: Coralife pump as seen under strobe lighting

Test Procedure

Before testing could begin on any of the pumps, an appropriate measurement time duration needed to be established to ensure that enough samples were taken to accurately represent the measured flow velocity and minimize measurement bias. To determine this duration, a value of the turbulence intensity was determined for several trials of differing time durations. The turbulence intensity FT is calculated using Equation 11, where is the standard deviation of the axial velocity and Vavg is the mean of the sample velocity.

FT =  σ / Vavg (8)

The turbulence intensity is a value representing the degree of unsteadiness or fluctuations in the measured flow field. An ideal steady flow with absolutely no fluctuations would have a turbulence intensity value of zero. When measuring unsteady flows, care must be taken to ensure that the fluctuations are accounted for and do not lead to temporal biasing of the mean velocity measurements. Theoretically, the mean velocity and turbulence intensity values will approach constant values as the sample time is increased to infinity. The reason for this is that as sample time is increased, any temporal bias in the measurement will be reduced.

During the test, two trials were averaged at various time intervals to produce the data shown in Table 4. The data was then plotted in Figure 9 to locate the "shoulder" of the curve, or the point that would produce reliable and accurate velocity data.

Table 4. Turbulence factors calculated for various time durations.
Turbulence Intensity Data
Time (sec) Sigma (ft/sec) V (ft/sec) FT
0 0.30 2.5 0.120
20 0.21 2.2 0.095
30 0.14 2.4 0.058
40 0.12 2.3 0.052
45 0.11 2.5 0.044
50 0.11 2.5 0.044
60 0.11 2.4 0.046

Figure 9. Turbulence Intensity plotted for various time durations

As shown in Figure 9, the point at which the turbulence intensity curve leveled off was found to be about 45 seconds. This duration was determined adequate to represent the velocity data for the pumps. For the extent of the test, velocity samples were taken using this time duration for sampling at each location.


Figure 10. Illustration of velocity measurement locations

With the time of each sample established, flow testing on the pumps could begin. The output nozzle diameter was measured for each pump and recorded for later use. Flow testing was broken down into two sets of trials for each pump: a horizontal set and a vertical set. The two data sets allowed the flow to be broken into four quadrants, providing a more accurate measure of the entire velocity profile. The data points taken are shown in Figure 10.

To begin taking data, the ADV was positioned such that the sampling volume of the measurement corresponded to the center of the pump output and was located one diameter downstream of the nozzle, as illustrated in Figure 5. The ADV was first positioned well outside the range of the flow, which was defined as a stagnant, or near zero, X velocity. The velocimeter was then moved in the positive Y direction across the velocity profile in 5mm increments until a non-stagnant X velocity was observed. Velocity measurements were then recorded for successive 5mm increments for the entirety of the profile until a stagnant velocity was reached at the corresponding location on the opposite side of the flow jet. This process was repeated moving the ADV vertically to achieve the measurements shown in Figure 10.

The raw data taken during the testing needed to be corrected before it could be used to calculate the volume flow rate. To begin, the velocity measurements taken from the velocimeter were in component form. The three velocity components (along the X, Y and Z axis) needed to be combined through vector addition in order to produce the final velocity measurement for the given location. This process is described through Equation 12, where Vtotal is the combined velocity, and Vx,y,z are the individual component velocities. This is an important step as the rotating propeller blades in many of the tested designs swirl the flow in a screw like fashion. The exit jet also expands as it leaves the pump. A simple one component velocity measurement may underestimate the actual water velocity.

Vtotal = (Vx2 + Vy2 + Vz2)1/2 (12)

The next modification to the data was made to "center" the measured points. This process was done to ensure that the velocity measurements taken matched up correctly to their radial location used in the flow calculation. Centering the data involved a set of criteria described below:

  • If the data contained an obvious flow deficit ("void") which represented the center of the propeller, the data was centered such that the void was assigned a radial position of 0 mm.
  • If the measured data did not contain an obvious flow deficit the data was centered symmetrically over a radial position of 0 mm.

To measure the rotational speed of the pumps, a small mark was painted on one side of the propeller, and the pump was turned on and set to the maximum speed. The strobe tachometer was positioned outside the aquarium facing the pump. The speed of the tachometer was adjusted until the mark on the propeller appeared stationary, and the RPM value displayed was recorded.

To measure the power consumed by each pump, the power source was run through the wattmeter shown in Figure 6. There was often a "settling" period observed where the pump initially drew slightly higher wattages, so the power value was recorded after taking the velocity measurements.

One exception made to this procedure was the measurements made on the MaxiJet 1200. This pump had an output diameter of less than ½", making measurement difficult at one diameter downstream. To compensate for the small output radius and ensure enough data points were taken, the ADV was positioned 1" downstream from the face of the pump. Due to the lack of a visual propeller on the MaxiJet, the pump speed was not measured.


Using the data collected, the flow profiles of the pumps was computed in the Z (vertical) and Y(horizontal) directions. The majority of the pumps tested produced nearly symmetric velocity profiles. Figures 11, 12 and 13 show the Ecotech Marine MP-60, the Tunze 6305, and the Hydor Koralia 8, respectively, which are examples of pumps that exhibited somewhat symmetrical flow fields. These figures show the results of both the horizontal and the vertical data sets for each pump. In these examples, it is seen that the MP-60 and Tunze 6305 produced a broad and comparably gentle flow, where the Koralia 8 produced a more concentrated jet with a higher peak velocity. The flow profiles for all the pumps is presented in Appendix 2. The reader should note the differences in complexity of the flow generated by the propeller generated pumps compared to that of a traditional impeller driven powerhead like the Maxijet 1200 (see Figure Appendix 2.7). The complexity of their exit flow field that makes simple single point measurement methods unreliable in determining rated flow rates.


Figure 11. Velocity Profile of Ecotech Marine VorTech MP-60


Figure 12. Velocity Profile of Tunze 6305


Figure 13. Velocity Profile of Hydor Koralia 8

Uncertainity and Error

While the Sontek specifications state a measured accuracy of +/- 1% of the reading, in actual situations this error will be higher. There are several sources of error and uncertainity that contribute to the flow calculations, some of which are listed below

  • Approximations used for integration depend on the granularity of data and number of points sampled
  • Unsteady nature of the flow field, due to blade wake passing, asymmetric or blocked inflow, inlet and exit grill interactions, ADV vibrations, etc.

While all the associated uncertainties are difficult to quantify without detailed analysis and huge investments in time and effort, based on our experience with flow measurements it is reasonable to expect that the error range of the calculated volumetric flow rates to be limited to 5-7% of the reported values.

Based on these flow profiles, the volumetric flow rate was calculated. The results are presented in Table 5. The column on the far right labeled "% Change from Manufacturer's Claim" is a comparison between the calculated experimental flow and the manufacturer's stated maximum output flow. This calculation is expressed by

equation (13)

Table 5 represents the data such that a positive change indicates an increase in the observed flow from the manufacturer's claim and vice versa. The data is shown graphically in figure 15.

Table 5. Test results for the various pumps at maximum power
Pump Pump Speed (RPM) Power Use (Watts) Calculated Flow (Gal/hr) % Change of Mean from Manufacturer's Rate
Aqueon 2400 3600 14.2 2744 14.30%
Coralife CP 2900 3600 18.8 2437.2 -16.00%
Hydor Koralia 5 3600 22 2597.59 57.43%
Hydor Koralia 6 3600 21.8 2205.6 0.30%
Hydor Koralia 7 3600 12 2659.1 -1.50%
Hydor Koralia 8 3600 18 3188.3 -1.90%
MaxiJet 1200 Unknown 20.7 405.7 37.50%
Tunze 6105 3250 24 2358.2 -31.30%
Tunze 6205 3160 45 3234 -44.30%
Tunze 6305 3060 48 3597.3 -54.60%
VorTech MP-10 3270 19.8 2460.3 56.20%
VorTech MP-40 2440 29 3781.2 18.20%
VorTech MP-60 2100 53 8509.8 13.5%

Figure 14. Comparison of Advertised Output Flowrates with Measured Output Flowrates

Another metric that could be use to evaluate the pumps is the Flow Efficiency, measured as the ratio of measured flowrate to actual power consumed. Table 6 and Figure 15 summarizes the flow efficiencies in units of GPH/watt. As shown, the pumps are broken into three different categories: AC (non-controllable), ACC (controllable), and DC (controllable). While the AC models offer better flow efficiencies, they do not offer the flexibility of output modification or advanced programming. The highest efficiency for the ACC pumps was the Hydor Koralia 7 and for the DC pumps was the Ecotech Marine Vortech MP-60.

Table 6. Summary of flow Efficiencies
Pump Flow/Power (GPH/watt) Power Type (AC/DC)
Aqueon 2400 193.2 AC
Coralife CP 2900 129.6 AC
Hydor Koralia 5 118.8 ACC
Hydor Koralia 6 101.2 ACC
Hydor Koralia 7 221.6 ACC
Hydor Koralia 8 177.1 ACC
MaxiJet 1200 19.6 AC
Tunze 6105 98.3 DC
Tunze 6205 71.9 DC
Tunze 6305 74.9 DC
Vortech MP-10 124.3 DC
Vortech MP-40 130.4 DC
Vortech MP-60 160.6 DC

Figure 15. Flow Efficiency of the Pumps Tested


A standard method for evaluating flow rates of pumps using ADV was developed, and applied to measurement of flow of several popular aquarium propeller pumps. Data obtained during this study shows that the generated flow field is more complex than a simple submerged jet and therefore single point measurements may not accurately represent the flow rate. After the completion of this experiment, it is clear that there is a difference between many of the measured results and their manufacturer's advertised performance. While most aquarium manufacturers are within a reasonable range of their claimed flows, there were some notable exceptions. As shown, measured values of volume flow rate for the Aqueon, MaxiJet, and EcoTech Marine models were generally higher than advertised flow outputs. The Hydor 6, 7, and 8 were measured to within 2% of the manufacture specifications. The Hydor 5 and Vortech MP-10 both presented an anomaly in that they produced 55-60% more flow than claimed. In fact, the Koralia 5 that was tested produced significantly more flow than the Koralia 6, and almost matched the output of the Koralia 7. The reason for this difference in claimed and experimental flow measurements is unknown.

On the other hand, for the Tunze units' measured flow rates were consistently under the advertised flow rates on the models tested. In the case of the Tunze 6305, the measured flow was less than half that of the manufacturer's claimed flow. Further investigation may be needed to determine how this manufacturer originally developed the advertised flow rates of each of its models (see Addendum).

Another conclusion that can be drawn from this experiment is that there is a wide range of flow efficiencies shown. The flow efficiency, or unit of flow observed per unit of power consumed, varies greatly from manufacturer-to-manufacturer and model-to-model. The flow efficiency values are presented in Table 6.



On completion of the study, the paper was sent to Tunze and Hydor prior to this publication. Based on these results, Tunze conducted its own independent tests on the Tunze pumps and have confirmed our results. On further discussion with Tunze we do not feel the errors were deliberate attempts to mislead, but rather their misguided faith in theoretical calculations that often do not translate well into real world application and use. In light of these finding Tunze is working to remedy the situation. For any resolution on how Tunze will address this please refer to Tunze's website for more information.


We would like to thank EcoTech Marine for providing the large aquarium and renting the equipment needed for the study. The work was performed under the technical guidance and consultation with Bill Straka and Sanjay Joshi of Penn State University. The data was collected by Mike Sandford during his summer internship at EcoTech Marine.


  1. Blevins, R. D., Applied Fluid Dynamics Handbook, Van Nostrand Reinhold Co., New York, 1984.
  2. Harker, Richard. "Product Review: Propeller Pumps In The Aquarium." Advanced Aquarist. Pomacanthus Publications, LLC. Web.,
  3. Riddle, Dana. "Feature Article: Measuring Water Movement in Your Reef Aquarium for Less Than $100." Advanced Aquarist. Pomacanthus Publications, LLC. Web., http://www.advanceda
  4. Taylor, John R. "Chapter 3." An Introduction to Error Analysis: the Study of Uncertainties in Physical Measurements. Sausalito, CA: University Science, 1997. Print.

Appendix 1: Example of Sample Data (Data Sample from Ecotech Marine Vortech MP-40)

Editor's note: The original article contained an embedded table that was to be displayed in-line with the article. Due to width constraints, we have instead converted this data into an image and are providing the data as an Excel spreadsheet and Adobe PDF.


Appendix 2: Plots of Velocity Profiles


Appendix 2.1. Velocity profiles of the Aqueon 2400


Appendix 2.2. Velocity profiles of the Coralife CP 2900


Appendix 2.3. Velocity profiles of the Hydor Koralia 5


Appendix 2.4. Velocity profiles of the Hydor Koralia 6


Appendix 2.5. Velocity profiles of the Hydor Koralia 7


Appendix 2.6. Velocity profiles of the Hydor Koralia 8


Appendix 2.7. Velocity profiles of the MaxiJet 1200


Appendix 2.8. Velocity profiles of the Tunze 6105


Appendix 2.9. Velocity profiles of the Tunze 6205


Appendix 2.10. Velocity profiles of the Tunze 6305


Appendix 2.11. Velocity profiles of the Ecotech Marine Vortech MP-10


Appendix 2.12. Velocity profiles of the Ecotech Marine Vortech MP-40


Appendix 2.13. Velocity profiles of the Ecotech Marine Vortech MP-60

No publisher Michael Sandford, William Straka, Sanjay Joshi Pomacanthus Publications, Inc. VorTech William Straka Sanjay Joshi Ph.D. Water Testing Water Circulation Product Review Michael Sandford Feature Article 2011-07-13T12:00:00Z Page
Product Review: Two Little Fishies' Media Reactor 150 and PhosBan Phosphate and Silica Adsorption Media TLF's 150 Reactor and PhosBan media performed as advertised. Under the conditions of this testing, both phosphate and silica concentrations fell to levels below the detection limits of 'laboratory grade' instruments. The successful application of these products in aquaria around the world is a testament to their functions. If you're battling algae outbreaks and need a quick solution, give these products a try. Click through to see the images.



Nuisance algae are perhaps the number one challenge facing aquarists and various strategies exist to prevent their growths. Pretreatment of makeup water (including reverse osmosis filtration, deionization), additions of high pH solutions of water and calcium hydroxide (kalkwasser), protein skimming, algal scrubbing with macro-algae, use of fish foods with low phosphorus content, etc. all can help control nutrients responsible for algal outbreaks. These methods have one thing in common - they target the element phosphorus.

Phosphorus is an element essential for all life forms including plants and algae. Indeed, bags of lawn fertilizer are marked with numbers (such as 10-5-5) indicating the amount of nitrogen, phosphorus, and potassium ('macro-nutrients'), respectively. If we were to remove or limit one of these macro-nutrients, we would be able to control the growth of plants and algae. This concept is known as Liebig's Law of the Minimum, which states plant growth is not encouraged by the total amount of nutrients available but instead by the one least available. Hence, phosphorus is often the element targeted for removal. Biological removal is possible, but requires a certain sequence of biochemical events. More often, phosphorus is removed by chemical means and is often done on industrial levels in wastewater treatment plants. It can be done in aquaria as well.

Recommended phosphate levels for reef aquaria vary somewhat although most are generally low (~0.03 ppm, or mg/l - 3 parts in 100,000,000 parts - quite low indeed).

Silica (SiO2) is of concern to hobbyists because it is used by diatoms to create their skeletons. Outbreaks of diatoms are characterized by brown coatings or filaments. While diatoms in themselves are not harmful (useless they smother sessile invertebrates) they can be unsightly. Some artificial saltwater manufacturers will not include silica in their mix. However, drinking water can often contain significant amounts of silica (~14mg/l). Since diatoms are photosynthetic, limiting phosphorus along with silica can control their population within aquaria. Silica can also 'plate out' on hot surfaces (such as heaters or pumps allowed to run dry) and can be difficult to remove.


Parts per million, essentially the same thing as milligrams per liter (mg/l)
A non-metal element considered essential for all life forms. It has an atomic weight of 30.9738 g/mol; its symbol is P.
Phosphorus bound with oxygen, and almost always the form of phosphorus found in aquatic environments.
Ortho-phosphate or reactive phosphate
This form is readily 'bio-available' for plant and algal growths and is the type measured by hobbyist test kits. It may be suspended or dissolved in the water column. Often reported as PO4-3, the recommended amount in a successful reef aquarium's water should be low (less than 0.05 ppm, or mg/l, if you prefer). When we consider that the phosphorus (P) portion of phosphate (PO4-3) is only about 1/3 of its weight, we can easily see that the 'reactive' part is only about 0.017 ppm. However, hobbyist test kits report ortho-phosphate as PO4-3; hence the recommended value is 0.05 ppm or less. To convert PO4-3 to P, divide by 3.066. To convert P to PO4-3, multiply by 3.066.
Total Phosphate
the sum of ortho-phosphate (easily measured) and that phosphate converted to ortho-phosphate by a severe digestion process employing potassium persulfate and sulfuric acid. Total phosphate can be suspended, dissolved, or incorporated in animal and plant tissues and is usually less bio-available for encouraging algal growths.


Two Little Fishies

Two Little Fishies, Inc. (or TLF, Miami Gardens, Florida USA) has been providing products to the pet industry since 1991. They offer a variety of products ranging from fish and invertebrate foods to aquarium supplements. Two of their offerings were selected for this month's Product Review - the PhosBan Reactor (model 150) and PhosBan phosphate/silica adsorbent.


PhosBan phosphate adsorption media.

The PhosBan reactor is a 'fluidized bed' (meaning the water to be treated flows upwards through the media and gently suspends at least some of the media particles). Treated water exits the reactor and returns to the aquarium. If all goes according to plan, the reactor's effluent will be depleted of phosphate and silica. How well do these products perform and are they worthy of your consideration? These are the recommendations made by TLF:

  • For use on freshwater or marine aquaria, up to 150 gallon (568 liter) capacity.
  • Flow rate through reactor should be 20 - 30 gallons (76 - 114 liters) per hour - this will require a pump capacity of 100 - 200 gallons (379 - 757 liters) per hour. A Maxi-Jet 500 (a misprint in the directions - a Maxi-Jet 400 or similar pump will work just fine) is recommended, but throttling will be required using the supplied ball valve. Excessive flow rates may cause the media to crumble - the directions use the synonym 'friable').
  • Reactor capacity depends upon the media. The 150 reactor can hold up to a maximum 200 grams of PhosBan media (5 inches or 12.7cm height within the column, with a recommended minimum of 2 inches or 5cm). The column can be filled to capacity when using granular activated carbon.
  • If an amount of PhosBan required is below the minimum depth within the reactor, TLF recommends mixing PhosBan with activated carbon.

Phosphorus Removal by Granular Ferric Oxide (GFO)

Iron particles possess a natural positive charge (these ions can have a valence of 2 or 3) while phosphorus possesses a negative charge. Since opposites attract, the phosphorus can be bound to iron (in this case, the ferric state, or Fe +3) thus removing it from solution and preventing it from fueling algal growths.

It is uncommon (and difficult) for hobbyists to distinguish between 'bio-available' phosphate (called 'reactive' or 'ortho-phosphate') and total phosphate (organically-bound) since the latter requires specific laboratory testing procedures and equipment. I wondered what impact PhosBan would have on organic phosphate concentrations and decided to test for it (see the 'Methods and Materials' section below for details). Figure 1 shows the results of testing for Total and Reactive ('ortho-') Phosphate over a period of 12 hours. Figure 2 demonstrates that, when ortho-phosphate content is subtracted from the amount of total phosphate, the level remains relatively stable, indicating removal of reactive ortho-phosphate only.


Figure 1. Time-course Reactive (ortho-) and Total Phosphorus removal by PhosBan. See Discussion section (below) for comments.


Figure 2. Total Phosphorus remained about the same during the experiment which is not surprising, as much of this element is probably found in suspended particles (algal cells, bacteria, food scraps) and not readily available to promote algae growths.

Silica Removal

TLF also claims that silica is removed by PhosBan as well. Figure 3 shows the results of testing 3 samples gathered over a 21-hour period after initiating treatment with PhosBan.


Figure 3. PhosBan quickly removes silica.

Effects on pH

A Hach HQ40d data logger equipped with a calibrated pH probe recorded pH values every five minutes over the course of 36 hours. pH fell slightly, but some of this drop is attributable to rising temperature (temp data not shown, and due to powerheads' operation within the aquarium). See Figure 4 and the Discussion section below for further comments.

The effects of PhosBan on alkalinity would be a better metric of its impact. See below.


Figure 4. pH of treated water fell over the course of 36 hours, but see comments in the Discussion section below.

Effects on Alkalinity

Directions for use of the PhosBan Reactor state that alkalinity will drop when 5x the recommended amount of PhosBan is used. Under the conditions of this experiment, alkalinity dropped by about 19% when PhosBan was applied at about twice the recommended amount. See Figure 5. At face value, this may seem negative until we consider that the presence of both phosphorus and silica lend to alkalinity (Standard Methods, 1998). Therefore, a portion of alkalinity drop could be attributable to their removal, and results generated by alkalinity testing in this situation could be partially attributed to removal of 'false' alkalinity and not a drop in carbonate content.


Figure 5. Alkalinity was negatively impacted when PhosBan was used at about twice the recommended amount (100 grams for 182 liters - 48 gallons) - but this is not necessarily a bad thing! Note that alkalinity was marginal to begin with. See text for details.

Water Color

Color of water can be estimated using a comparator or a colorimeter/spectrometer. Color is due to dissolved organic substances (called gelbstoff, German for 'yellow matter') in the water column. Generally, color due to these substances is yellowish and is reported in Platinum/Cobalt units. A few milligrams of dry PhosBan was placed in a beaker containing 100ml deionized water and allowed to sit overnight. A sample was analyzed for color (at 455nm). PhosBan did not impart color to the water.

On the other hand, GFO has the potential to remove organic substances causing yellow water. This was not tested.

Discussion and General Impressions

The PhosBan Reactor 150 is constructed entirely of plastic and acrylic materials and is safe for use in freshwater and saltwater applications. The clear acrylic material of the reactor itself appears to be about 1/16" (~1.6mm) thick and is rugged enough to withstand some abuse. The 90°elbows fitting the barbed fittings atop the reactor are made of a soft rubber-like material and are friction fits. Use cable ties to affix these 90's to the reactor if desired - avoid stainless steel worm clamps that might compress and break the barbs.

This reactor holds about 36 fluid ounces (1,075ml) and has a useable capacity of about 26.5 fluid ounces (~785 milliliters). Assuming PhosBan has a consistent density, the 150 reactor will hold approximately 7.3 ounces (207 grams) of this material. Using the manufacturer's recommendations for loading, the reactor will hold enough PhosBan to treat a maximum marine aquarium size of 200 gallons (757 liters; using 50 grams for 50 liters). It should be sufficient to treat a 400-gallon (~1,500 liter) freshwater aquarium. Note that these ratings are higher than TLF's recommendation of a maximum aquarium size of 150 gallons.

Under the conditions of these tests, TLF's 150 Reactor containing PhosBan quickly removed both phosphates and silica to levels below the detection limits of the spectrometers (for our purposes, the concentration of both silica and ortho-phosphate fell to 'zero').

GFO can potentially remove other chemicals including cobalt, manganese, zinc and nickel (Holmes-Farley, 2008). All (save the latter) are important micronutrients for algal growth. The effectiveness and rapidity of GFO in sequestering these is unknown to me.


  • Reactor is well made yet relatively inexpensive
  • Media is relatively inexpensive and lives up to manufacturer's claims
  • Ortho-phosphate and silica are effectively and quickly removed to levels approaching zero
  • Recommended pump (Maxi-Jet, not included) is readily available, reliable, inexpensive to purchase and operate
  • Device (ball valve) to regulate water flow through the reactor is included
  • Directions are appropriate and easy to follow
  • The reactor can be used with other media, such as activated carbon


  • Effectiveness of any GFO product in removing some 'trace elements' (Mn, Zn, Co, for example) from artificial seawater is unknown
  • Instructions not available on TLF's website (I routinely misplace directions and did so for a while during the course of writing this article)



There is some concern about depleting reactive phosphate levels too quickly and/or for extended periods of time (remember Liebig's Law of the Minimum discussed earlier). Proceed slowly with the application of any product in a reef aquarium and closely watch corals for negative reactions.

While reactive phosphate is effectively removed, the same cannot be said about the form of phosphorus (acid hydrolysable) that requires vigorous laboratory digestion processes before analysis. Information suggests that almost all of the acid-hydrolysable phosphorus is suspended - not dissolved - in the water column and this form should not be of much concern to hobbyists.

The media reactor is well made and should provide years of service. The adsorption material is relatively dust-free (although it should be flushed with water per the manufacturer's recommendations) and has not crumbled and added any apparent particulates or color to the aquarium water. In addition, there were apparently no significant negative impacts on water chemistry even when used at twice the recommended amount (however I would strongly advise hobbyists to follow the manufacturer's directives).


Materials and Methods

A 55-gallon (208 liters) was filled with 48 gallons (182 liters) of well-aged artificial seawater from a fish-only aquarium. A PhosBan Reactor 150 was installed according to manufacturer's recommendations. Since the suggested amount of PhosBan for 48 gallons of seawater did fill the reactor to the minimum recommended level, the dosage was doubled to 100 grams of PhosBan phosphorus adsorbent to fill the reactor to the recommended depth of 2 inches (~50mm). A Maxi-Jet 400 provided flow, which was regulated to 19.6 gallons per hour (~1,240 milliliters per minute) using the supplied in-line ball.

Baseline water samples from the aquarium were gathered in PO4-3-free bottles, and again at 0.5, 1, 2, 3, 11.5, 21, and 36 hours after starting the reactor's pump. These were analyzed for Total Phosphorus and Reactive Phosphorus using a Hach 2800 Spectrometer, DRB 200 Dry Thermostat Reactor, and reagents from Hach (potassium persulfate and sulfuric acid for digestion, and ascorbic acid method for analyses). Hach advertises the range of the ortho-phosphate analysis to be 0.02-2.50 ppm and total phosphate as 0.06-3.50 ppm (both expressed as PO4-3). Alkalinity (as calcium carbonate; CaCO3;) was determined using a Hach Digital Titrator and alkalinity reagents, using a calibrated pH meter and probe to determine titration endpoints (which varied from 4.5 to 4.8, depending upon phosphate concentrations and the presence or absence of silica) . A Hach HQ40d data logger equipped with a pH probe measured and recorded pH and water temperature every 5 minutes. Silica was determined by a LaMotte Smart2 colorimeter using LaMotte silica reagents (high range - 0-75 ppm, using ammonium molybdate in an acidic state, with oxalic acid added to prevent a reaction with phosphate and molybdate).


  2. Holmes-Farley, R., 2008. Reef Alchemy: Iron oxide hydroxide (GFO) phosphate binders. Reef Keeping Magazine Online.

No publisher Dana Riddle Pomacanthus Publications, Inc. Product Review Dana Riddle Phosphate GFO Phosphates Granular Ferric Oxide 2011-06-15T12:00:00Z Page
Aquarium Chemistry: The Nitrogen Cycle: New Developments and New Prospects So far we have always thought of the nitrogen cycle as a series of linear reactions that conclude in a circle. But is it really a cycle? Important discoveries made in these recent years have drastically revolutionized this concept. In this article, I will try to discuss some of these research studies, with the intention and hope of being able to make this complex topic, understandable. Click through to see the images.


The nitrogen cycle plays a highly important role in a closed environment like that of an aquarium. Due to its presence, it is possible keep the fish and invertebrates alive, in a small viable space, therefore it is fundamental to learn to know it, mainly in respect of the life forms that we nurture.

Until a few years ago, it was thought that the nitrogen cycle in its complexity, was a complete linear process. However, most recent scientific discoveries have greatly revolutionized our well-established knowledge on the nitrogen cycle and on the micro-organisms involved in such processes. As a matter of fact, the global cycle of nitrogen in the environment, particularly in that of marine, has been integrated with at least three new links which include:

  1. the oxidation of ammonium by a particular group of micro-organisms, the archaeabacteria (AOA);
  2. the anaerobic reduction of nitrates into ammonium ion (DNRA);
  3. the anaerobic oxidation processes of ammonium (ANAMMOX).

In the first part of this article, I will try to review the essential and more predominant aspects of the nitrogen cycle: the transformation processes of the main components (atmospheric nitrogen, ammonium ion, nitrite, nitrate) and the role played by the bacterial species involved.

In the second part, new ways will be explored with particular reference on the role of bacteria, focusing on the implications that these new discoveries have brought in the global cycle of nitrogen.

The Canonical Nitrogen Cycle

Nitrogen (N) is an essential nutrient for all organisms, and it is a critical element of protein, vitamins and DNA, and is important in biochemical structures and process that define life.

Nitrogen exists in different states of oxidation and in many chemical forms and is quickly converted by the microorganisms both on earth and the sea.

In the marine environment, nitrogen is present in 5 forms:

  1. Gaseous nitrogen (N2), stable molecules that require specialized enzyme systems (present in some types of bacteria) for fixation and later use;
  2. Ammonium ion (NH4+), the most reduced natural specie of nitrogen, and the most biologically available in an oxygen-less environment;
  3. Nitrate ion (NO3-), the most oxidized form of nitrogen and mostly usable in an aerobic environment;
  4. Particulate organic nitrogen (PON), organic form of nitrogen predominant in sediments;
  5. Dissolved organic nitrogen (DON), a rich mixture of molecules with a wide range of composition.

A complex network of reactions links these nitrogen forms in processes that as a whole, is called the nitrogen cycle (Figure 1). The greatest source of nitrogen comes in the form of inert gas N2 (N ≡ N), representing 78% of the atmosphere. A small part of the atmospheric N2 is fixed by particular bacteria called nitrogen-fixing (nitrogen fixation) and is reduced to ammonium ion (NH4+) which can be easily usable for other organisms. In a marine environment which inhabited by particular bacteria, ammonium is quickly oxidized to nitrate in aerobic conditions (nitrification). Nitrate is then reduced again to an N2 gas in anaerobic conditions (denitrification), thereby completing the cycle (Figure 1).


Figure 1. Diagram of the marine nitrogen cycle.

Nitrogen Fixation and Ammonification

Nitrogen fixation

The biological fixation of nitrogen can be synthetically represented by the following global formula:

N2 + 8H+ + 6e- 2NH4+

Which means that for each molecule of atmospheric nitrogen, 2 ammonium ions are formed with the absorption of 6 electrons and 6H+, this last process tends to increase the pH.

It is interesting to note that, ultimately, the ammonium ion in the water is in balance with ammonia (NH3) based on the following stoichiometry:

NH3 + H2O ↔ NH4+ + OH-

The concentration of the two chemical species relies largely on the pH, in short, the higher the alkalinity, the larger will be the quantity of ammonia; or proportion-wise, the lower the pH is (more acid), the larger will be the quantity of ammonium ion (less toxic than ammonia). As can be seen in Figure 2, in an average range of pH in the seawater, the percentage of NH4+ is higher (82-97%) compared to that of NH3 (3-18%).

As we have previously stated, the atmospheric nitrogen N2, before being incorporated into the biological molecules, has to be reduced to NH4+, through a series of reactions called biological fixation of nitrogen. Such reactions are catalyzed by a particular enzyme, nitrogenase, which is present in some nitrogen-fixing bacteria belonging mainly to Cyanobacteria phylum. One of the peculiar characteristics of this enzyme is that it comes irreversibly inhibited by the molecular oxygen (O2); and since fixation is a process that happens in an aerobic environment, it creates an apparent paradox. In reality, cyanobacteria are able to negotiate the activities of nitrogenase, an enzyme which is essentially anaerobic, with the inevitable presence of oxygen (resulting from photosynthetic processes), through not yet well-known mechanisms. In the marine environment, the nitrogen-fixing bacteria (some of which also belong to Clostridium and Azobacter genera) can be found both in free form and in symbiosis with other organisms (ex. Sponge).

But what is the source of nitrogen in an aquarium? Certainly, the biological fixation of nitrogen is an extremely important process in the ocean, but it has a limited role in the tank.


Figure 2. pH-dependent concentration of NH4+ and NH3 in the seawater

The main source of nitrogen is obtained from the nourishment both of the fish and invertebrates, particularly in the form of protein and single amino acids, assuming they are directly administered into the tank. Even minor vitamins and other molecules like the DNA, contain nitrogen but the quantity is decisively less than that of protein's. In proteins, nitrogen forms a part of the framework and of some single amino-acids' lateral chains, as the tryptophan, asparagin, glutamine, lysin, arginine, histidine.

The oxidative degradation of amino acids leads to the release of ammonia nitrogen into the tank. In what way? On one hand, the protein ingested by the fish or by the other organisms are broken down into single amino acids. In turn, amino acids can be used to build new proteins within the organism or be oxidized to supply energy. The degradation of amino acids by the animals leads to the elimination of varied by-products. For example, the fish release nitrogen as ammonia, while the majority of organisms may release it in the form of uric acid (fowls, reptiles), or urea (humans). On the other hand, in the presence of a strong organic charge, protein and amino acids in waste products, in sediments and in organic decay are decomposed in a process called ammonification, carried out by particular decomposer bacteria which release ammonium into the water by degrading the aminoacidic nitrogen.


Nitrification occurs in two distinct stages:

  1. oxidation of ammonium to nitrite (nitrosation) and
  2. oxidation of nitrite to nitrate (nitration).

1) Nitrosation: in the first stage, ammonium ion is oxidized to nitrite in two steps:

  1. The first step is catalyzed by the enzyme, monooxygenase which forms the hydroxylamine by using O2 as oxidant:
    2NH4+ + O2 → 2NH2OH + 2H+
  2. In the second step, hydroxylamine is oxidized to nitrite by the enzyme hydroxylamine-dehydrogenase:
    2NH2OH + 2O2 → 2H+ + 2H2O + 2NO2-

2)   Nitration:  the oxidation of nitrite to nitrate, which occurs through the activity of the nitrite oxidase enzyme, completes the process of nitrification:

2NO2- + O2 → 2NO3-

The conventional view of nitrification occurs in the presence of oxygen and anticipates the oxidation of ammonium to nitrate based on the following global synthetic formula (see Figure 1):

2NH4+ + 4O2 → 4H+ + 2H2O + 2NO3-

But who directs the music? The metabolic work of nitrification is entrusted to two groups of nitrifying bacteria:

  1. bacteria which oxidize ammonium (ammonia-oxidizing bacteria or AOB), also called nitrous bacteria. They belong chiefly to the Nitrosococcus and Nitrosomonas species;
  2. bacteria which oxidize nitrite (Nitrite-oxidizing bacteria or NOB) also called nitric bacteria. They form a part of the Nitrobacter, Nitrococcus and Nitrospina species.

The nitrifying bacteria are generally obliged aerobes and obliged chemoautorophs because they directly use CO2 as a source of carbon, while organic substances can be toxic.


Here I describe the four stages of denitrification process in detail. The oxidation state of nitrogen is indicated by the enclosing parentheses, after the names of chemical species.

  1. Reduction of nitrate (+5) to nitrite (+3). This reaction is catalyzed by nitrate reductase (NAR) which exists in the (internal) cytoplasmic part of bacterial membrane. Nitrate is carried within the bacterial cell by a specialized carrier (AP in Figure 3), defined as antiport because it exchange ion nitrate upon entry with the nitrite which is produced in the reaction and must be carried to the (external) periplasmatic space for the subsequent reaction.
    2NO3- + 4H+ + 4e- → 2NO2- + 2H2O
  2. Reduction of nitrite (+3) to nitric oxide (+2). The nitrite which is now at the periplasmatic space is reduced by nitrite reductase (NIR), releasing nitric oxide (NO). NO is a remarkably important molecule, from the bacteria to humans (but this is another story).
    2NO2- + 4H+ + 2e- → 2NO + 2H2O
  3. Reduction of nitric oxide (+2) to nitrous oxide (+1). NO is reduced by nitric oxide reductase (NOR) to nitrous oxide (also called nitrogen protoxide otherwise known as the laughing gas). Both oxides represent a strong stimulus to the reductase synthesis in the presence of nitrates and under anaerobic conditions.
    2NO + 2H+ + 2e- → N2O + H2O
  4. Reduction of nitrous oxide (+1) to gaseous nitrogen (0). The last reaction in the denitrification process is the reduction of nitrous oxide to molecular nitrogen in gaseous form by the nitrous oxide reductase. This reaction should complete the denitrification process and conclude the nitrogen cycle.
    N2O + 2H+ + 2e- → N2 + H2O

Denitrification is one of the key processes within the nitrogen cycle and anticipates the reduction of nitrates to gaseous nitrogen, passing through nitrite, nitric oxide (nitrogen monoxide) and nitrous oxide (nitrogen protoxide).

The global reaction of denitrification (without considering the organic molecular degradation eventually associated) can be synthesized with the following formula (for details see Figure 1):

2NO3- + 12H+ + 10e- → N2 + 6H2O

Denitrification is mainly a heterotrophic option and occurs in anaerobic conditions. A wide range of bacteria called precisely denitrifying bacteria are able to carry out the entire sequence of reactions, being equipped with a complete enzyme apparatus.

The denitrifying bacteria are able to accomplish the anaerobic respiration of nitrates by using the nitrate in place of oxygen, as acceptor of the electrons released during the respiratory process. These bacteria possess special enzymes (Figure 3), as the nitrate reductase (NAR) and nitrite reductase (NIR), which allows the electrons to flow towards nitrate or nitrite, in the absence of oxygen. They are flexible enzymes which form in the cellular membrane only under anaerobic conditions: as a matter of fact, a part of NAR, the reductase synthesis is inhibited in the presence of oxygen.

Some bacterial species of the Pseudomonas, Thiobacillus, Paracoccus and Naisseria classes, are considered denitrifying.


Figure 3. Denitrification process on the bacterial membrane.

New Developments and New Prospects

The previous description represents a well-known scenario for a long time. In the course of the recent years however, our references concerning the nitrogen cycle have drastically changed to the extent that the principle of closed linear cycle itself is being questioned. This is because new reactions have been discovered and consequently new microorganisms that make the entire nitrogen cycle even more complex and twisted (Figure 4). In the second part of this article, I will try to clarify some important ways which will be inserted within the canonical nitrogen cycle:

  1. Ammonium oxidation by a particular group of microorganisms, the archaeabacteria (AOA)
  2. The anaerobic reduction of nitrates to ammonium (DNRA):
  3. The anaerobic oxidation processes of ammonium (ANAMMOX)

AOA: Ammonium Oxidizing Archaeabacteria

Recently, new important components of nitrogen cycle, which form the part of the richer and diffused group of micro-organisms in the planet, the archaeabacteria, have been identified. In spite of the group's evolutive line being unclear, the archaeabacteria (Archaea or Archeobacteria) combined with the eukaryotes and with eubacteria, are some of the fundamental domains of the living beings.

The archaeabacteria, like the bacteria, consist of single cells without nucleus and in the past they were classified as prokaryotes together with the bacteria. Based on the DNA analysis, the archaeabacteria were re-grouped into three phyla: Crenarchaeota, Euryarchaeota and Korarchaeota. The Euryarchaeota bacteria are the most prominent and they include methane producers and holophiles. The Crenarchaeota bacteria include thermophilic microorganisms, while the Korarchaeota bacteria are less known because only their DNA is recognized but no microorganism has so far been isolated. Originally, it was thought that the archaeabacteria were just inhabitants of a harsh and most hostile environment on the face of the earth. The thermophiles can grow at a temperature higher than 100°C, the psychrophiles are those which grow at temperatures lower than -10°C, while the acidophilus and the alkaliphiles grow in extremely acidic or alkaline environments, respectively. Finally, the halophiles prefer the highly saline environment. Today, we know that archaeabacteria are present in all habitats: for example the Crenarchaeota bacteria are considered ubiquitous components of zooplankton.

In 2004, a particular gene called the ammonium mono-oxygenase (amoA) was discovered in marine Crenarchaeota, indicating the capacity to oxidize ammonium. The definite and convincing link between this new gene and the ammonium oxidation in archaeabacteria has been recently established in Crenarchaeota, the Nitrosopumilus maritimus, which was isolated from the water of aquarium. N. maritimus is chemoautrophic: as a matter of fact it grows with bicarbonate as the only source of carbon (organic carbon inhibits its growth) and converts NH4+ in NO2- (green line in Figure 4 and Figure 7). Other archaeabacteria have been successively identified with this property and have been named as Ammonium oxidizing archaeabacteria (AOA). An accurate analysis of the AmoA gene in many archaeabacteria has revealed diverse isoforms of this gene, each one is associated to a microorganism which is present in different habitats (with little overlapping, for example, between sediment and water column). Symbiont archaeabacteria have also been identified, like for example the Cenarchaeum symbosiosum, a symbiont Crenarchaeota with a sponge. Surprisingly, it was observed that this archaeabacteria is not able to produce hydroxylamine as intermediate reaction (see the Nitrosation process in the BOX 2) indicating that ammonium oxidization occurs with a mechanism which is different from that of the classic nitrification. Finally, the most recent studies conclude that the majority of Crenarchaeota are AOA's and AOA's are microorganisms whose presence is numerically predominant in the ocean.


Figure 4.Nitrogen cycle integrated with recently discovered reactions. Nitrogen oxidation states are pointed out.


Figure 5. The life tree. Evolving lines of the main domains.


During the recent years, the anaerobic reduction of nitrates/nitrite or, DNRA (acronym for Dissimilatory Nitrate/nitrite Reduction to Ammonium) has stirred up a certain interest as a relevant reaction both in the terrestrial and marine eco-systems. The reaction has been described in anoxic sediments and in the presence of bacteria of the Thioploca and Thiomargarita species. Both types of bacteria are able to concentrate nitrates within their own cells for the subsequent oxidation of sulphur-containing compounds in reduced form. In this way, they are able to reduce nitrate to ammonium passing through nitrite as an intermediary compound (blue line in Figure 4 and Figure 7). This reaction, although still needing clarification, would potentially supply nitrite and ammonium to the ANAMMOX reaction (see subsequent paragraph) in anoxic sediments.

ANAMMOX: anaerobic ammonium oxidation

As we have previously seen in the description of AOA and nitrification stages, ammonium oxidation is a strictly aerobic process. In reality, we have also seen that ammonium can be generated in hypoxic and anoxic environment (for example in sediments) through the re-mineralization of organic nitrogen process (ammonification), and/or the anaerobic nitrite reduction (DNRA). For many years, it has been thought that ammonium is inert in anaerobic conditions, which is to say, useless for living things. The problem, however, is that no bacteria that are able to metabolize ammonium without oxygen have been identified, especially due to the technical difficulty of cultivating in the laboratory bacterial strains with these characteristics. In 2008, many of these difficulties have been overcome and some laboratories were able to identify, cultivate and characterize some types of ANAMMOX bacteria (Acronym for ANaerobic AMMonium OXidation) which are capable of oxidizing ammonium to gaseous nitrogen (N2) (red line in Figure 4 and Figure 7) by using nitrite as electron acceptor, instead of oxygen.

The first bacteria that are isolated in a marine environment belongs to the Scalindua species (Sc. sorokinii) although a probe regarding the presence of other species like Brocadia and Kuenenia, is being conducted. The common characteristic of these bacteria, unique in its class, is the presence of a specialized organelle called anammoxosoma which is surrounded by a particular lipid (fat) that contains hydrazine oxide reductase, an exclusive enzyme which is able to combine nitrite and ammonium is a single step (Figure 6). These bacteria use a rather complex mechanism that involves hydrazine as an intermediary. However, the following reaction, which is incomplete and stoichiometrically unprecise, can suggest the idea of an ANAMMOX process.

NH4+ + NO2- → N2 + 2H2O

This reaction has been described for the first time in sediment samples taken from particular marine ecosystems (the Black Sea, for example). It has been observed that in those experimental conditions, the ANAMMOX process was responsible for the loss of 30-50% of inorganic nitrogen from the sea (in the form of N2), significantly making it of the same level as the classic denitrification. But to analyze it closely, if we associate the above-mentioned DNRA process with ANAMMOX, we have a real and actual anaerobic denitrification, clearly not canonical. Indeed, DNRA supplies nitrite (as a reaction intermediary beginning from nitrate) and ammonium (the latter having been obtained also through organic nitrogen ammonification), and ANAMMOX transforms everything into gaseous nitrogen. A lovely and good denitrification, clearly with different mechanisms and bacterial strains, but nevertheless, a denitrification.


Figure 6. ANAMMOX Bacterium

The question now is: under analogous conditions, can ANAMMOX occur in an aquarium? Obviously we are not able to establish that but we can make some considerations. A driven DSB can reproduce optimum conditions for this process. In fact, nitrogen bubbles are visible in the depths of the sediment. In line with this, it has been experimentally observed (but not in an aquarium) that the higher the layer of sediment, the more pushed the anoxic condition (oxygen inhibits the reaction) and the faster is the reaction. Therefore the high efficiency of a DSB in removing nitrates can be also due to a non-canonical denitrification, besides the classic anaerobic denitrification; obviously, the eventual presence of qualified bacterial strains has yet to be defined. Figure 7 illustrates the schematic diagram of integrated nitrogen cycle with the new reactions and the areas in which they occur.


Figure 7. Nitrogen cycle as revised and integrated. Areas where reactions occur are made evident.

In conclusion, these constant discoveries clarify many obscure points of the nitrogen cycle but at the same time they open up new horizons and paradigms that make these processes even more complex and fascinating. On the other hand, I hope not to have further complicated the well-established ideas on nitrogen cycle, with this article. I also wish that over time, these new discoveries can be applied and integrated with the aquarium, in spite of the scarce scientific researches in this area. However, even if just theoretical, this knowledge allows us to better understand that which can occur in our tanks and nurture our passion for aquarium.


  1. Arrigo K. R. (2005) Marine microorganisms and global nutrient cycles. Nature 437: 349-355.
  2. Berman-Frank I., Lundgren P., & Falkowski P. (2003) Nitrogen fixation and photosynthetic oxygen evolution in cyanobacteria. Res.Microbiol. 154: 157-164.
  3. Brandes J. A., Devol A. H., & Deutsch C. (2007) New developments in the marine nitrogen cycle. Chem.Rev. 107: 577-589.
  4. Francis C. A., Beman J. M., & Kuypers M. M. (2007) New processes and players in the nitrogen cycle: the microbial ecology of anaerobic and archaeal ammonia oxidation. ISME.J. 1: 19-27.
  5. Jetten M. S. (2008) The microbial nitrogen cycle. Environ.Microbiol. 10: 2903-2909.


Marco Colasanti aka marcola62 (moderator of Reefitalia forum). A special thanks is owed to the staff of ReefItalia community for their support.

About the Author

MARCO COLASANTI, born in Rome, Italy, September 15, 1962, has a degree in biology and holds a Ph.D. in Neuroscience. He is currently a Full Professor in Cell Biology at the Department of Biology, Faculty of Sciences of the University of Rome, ITALY. Entrusted with holding courses of Cellular Biology and Laboratory of Cellular Biotechnology for the University Degree of Biology. He entered the aquarium hobby with freshwater tanks (1982) and set up his first saltwater tank in 1995. He is currently a Staff Member as a Moderator of ReefItalia, an Italian reef community. Over the last fifteen years, active in the scientific research on Nitric Oxide (NO) pathway in different models and systems, including fish and invertebrates. Co-author of more than 70 publications in international peer-reviewed ISI journals or books.

No publisher Marco Colasanti Pomacanthus Publications, Inc. Marco Colasanti Aquarium Chemistry Nitrates 2011-04-19T12:00:00Z Page