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Reef Aquarium Chemistry Maintenance


By Carl Strohmeyer-PAMR 38+ years experience

Updated 1/8/2017

Marine Fish, Reef Aquarium Chemistry


Calcium is an essential element required by our reef aquarium. It is the building block for many hard corals, but is still required by all reef inhabitants, even fish! Your reef aquarium calcium level should be 400-450 ppm.
Since fish in marine environments constantly drink the water around them, they have a chemistry that is in sync with their environment.
A regular dosing/supply of calcium also supplies essential mineral Cations that again all reef inhabitants require.

Further Reading:
*Do Fish Drink? Osmoregulation in Fish
*Aquarium Redox, Including Cation replacement

Use of popular Calcium Chloride Dehydrate products only or along with economy Soda Ash Sodium Carbonate products sold by discount bulk suppliers can result in a slow build up of sodium chloride even with a stable specific gravity or salinity, resulting in less than optimal ionic balance for your reef aquarium.

This is where the 3 step Balling Method is superior as no additional Sodium Chloride is added nor is it concentrated.
The Balling method also eliminates the use of a calcium reactor.
By not using a calcium reactor, this creates some other benefits:
  -The addition of the balling mix provides all the depletion of elements.

Video explaining the "Balling Method":
The Balling Method explained by Hans-Werner Balling
The Balling Method explained by Hans-Werner Balling

Calcium, Reef Advantage, Balling Method for marine aquarium chemistry Recommended Product Resources (sponsors this hobby with websites such as this):
*AAP Bio-Calcium Original Balling Set; Parts A/B/C.
*SeaChem/AAP Reef Advantage Calcium

Other methods of calcium maintenance include Kalkwasser, Calcium reactors, and products such as "Reef Calcium; polygluconate".

While Kalkwasser is popular among many advanced marine aquarists, caution should be used with this method of adding calcium to your marine aquarium. This is not to say Kalkwasser does not work, in fact introduced properly it is an excellent way to regulate calcium and alkalinity in saltwater aquariums.

Here is how Kalkwasser works:
Used properly Kalkwasser (Calcium Hydroxide) is slowly dripped into your aquarium, it captures free Carbon Dioxide present in the tank water and converts it to Bicarbonate ions.
However if you drip too fast or if there is not enough Carbon Dioxide available in the water, Carbonate ions will be formed which will make the Ca++ you are trying to add to your tank get wasted by the useless precipitation of Calcium Carbonate (often forming a white residue that precipitates out of your aquarium).
This too rapid addition of Kalkwasser may actually cause the Calcium and Alkalinity in your tank to go down instead of up.
See the equation below:
Ca++ + 2(HCO3-) + Ca++ + 2(OH-) <==> 2 CaCO3 + 2 H2O

Often even a slow drip of Kalkwasser (Calcium Hydroxide) can cause the above reaction if there is not enough CO2 present in your marine aquarium.
One method to avoid this is to add 15ml of 5% Distilled White Vinegar (Acetic Acid) into a 1 liter or 1 quart container.
Dissolve 1/2 teaspoon of Kalkwasser into the Acetic Acid, and then dilute to 1 liter (1 quart) volume with either RO/DI water (tank water can be used in a pinch).

A Calcium Generator/Reactor is another popular method for maintenance of calcium and alkalinity as well as KH/pH regulation, especially in marine/reef tanks heavily stocked with stony corals.
A calcium Reactor works by providing a steady stream of calcium (and some Strontium too) by using CO2 in the reactor. The CO2 then "reacts" with the Calcium Carbonate producing calcium ions and carbonate ions (the carbonate ions increase alkalinity).
Although I have NOT had an instance where this was an "essential" device for my reef tanks, it can be very useful for previously noted reasons.
I have also had issues of too much CO2 getting into the marine/reef aquarium resulting in drops in pH and Alkalinity. This is not to say CO2 is "bad" for a marine/reef aquarium as it is needed for photosynthesis in the same way it is needed in a freshwater planted aquarium, however a CO2 level that constantly crashes your pH/Alkalinity is simply too much CO2!

Under normal circumstances/conditions a Fluidized Filter utilizing Oolitic sand media can accomplish similar results, however for high bio load reef tanks with large amounts of stony corals, a Calcium Reactor will produce more calcium.

Reef Aquarium Chemistry Maintenance
Kalkwasser and Calcium Reactor Information Referenced from:
*Aquarium Chemistry; Use Of Kalkwasser, Calcium Reactors

Resource for basic but accurate Calcium Test Kit:
API/AAP Calcium Test Kit

Resource high performance Fluidized Sand Bed Filters:
Fluidized Sand Bed Filters from AAP


Which is better Sodium Carbonate vs Bicarbonate?

First what is the chemical difference:
Sodium Carbonate = CO3--
Sodium Bicarbonate = HCO3- (the "Bi" means two, as in H + CO3)

Next, a little about pH since alkalinity is what generally stabilizes pH in our aquariums. pH = a measurement of H+ and the more H+ the lower the pH and less Alkalinity in short. Molar value wise, it takes twice as much as Bicarbonate as Carbonate to raise the Alkalinity up 1 Equilibrium unit. Volume wise it is 0.6 tsp of Bicarbonate vs. 0.4 tsp of Carbonate to raise the Alkalinity 1 milliequivalent (mEq) / or 2.8 dKH in 10 gals. Weight wise, is it is 3 grams vs. 2 grams.

Bicarbonate, due to that H, has less impact on pH than Carbonate.
Bicarbonate is mostly for raising the Alkalinity along with pH maintenance, while Carbonate is for raising the Alkalinity and pH.

Carbonate used only by itself should only be used if you have a low pH and Alkalinity. If it's to buffer up the Alkalinity, Bicarbonate is better.

Generally in a healthy/balanced reef aquarium where excess CO2 is not being produced or introduced (such as with a Calcium Reactor), a Bicarbonate is the better choice for an ionically blended bicarbonate with other elements in ionic balance such as SeaChem/AAP Reef Builder, NOT an economy Soda Ash Sodium Carbonate.

Recommended Product Resource (sponsors this hobby with websites such such as this):
SeaChem/AAP Reef Builder

Sodium (Na+) more or less accumulates over time, as does the SO4 and Chlorides from non-ionically balanced use of calcium supplements, alkaline buffers, and minor/trace elements. This is why water changes are often needed to keep the chemistry in balance even though specific gravity/salinity is "spot on". Hence my recommendation of the AAP Balling Method or ionically SeaChem supplements.

It is common for the pH to drop over night, especially if the alkalinity is less than 8 dKH. This pH drop is from animals and plants giving off CO2 at night. The reason why it may not hold at a lower Alkalinity is also a night thing of animals and plants "leaching" out things more so, which can have a greater impact on the Alkalinity and pH as they yield acids.
A common limnological [1] term for Alkalinity is ANC ("Acid Neutralizing Capacity"). These affect the pH and Alkalinity. Although it's not often heard of in the aquarium keeping hobby, there's also Acidity, BNC, ("Base Neutralizing Capacity"). It's the opposite of Alkalinity.

Recommended discussion:
Sodium Carbonate vs Bicarbonate; from Manhattan Reefs

[1] "Limnology": The scientific study of the life and phenomena of fresh water, especially lakes and ponds (Adj. limnological - of or relating to limnology).


Many trace and some minor elements are not depleted at the same rate as alkalinity and calcium. In my experience not every reef or even marine fish/FOWLR aquarium is the same when it comes to depletion of trace, minor, or major elements.
There is also disagreement among many with what is a minor, trace or major element with websites such as "Live Aquaria" calling Strontium a major element, where as based on its percentage it clearly falls into the category of minor or trace element.


Regardless of what we call each element, it's important to keep your reef or even fish only marine aquariums as close to natural percentages as possible. Although we often find keeping Calcium slightly higher works to our advantage in the closed system most any marine aquarium is in reality.

Recommended Reef Chemistry Calcium Method, 3 Part Balling
For this reason, we need to find a method, which works best for us AND our aquarium, not what seems like the method de-jour of the day. As well, just because something might seem more complex, does not necessarily make it better either. So, if you are a beginner, do NOT feel pressured by the so-called pros in many forums, which insist that it's their way or the highway (this is also not to say their method does not work, only that often these over involved methods do not work any better than more simple methods).

As noted earlier, also be careful of popular economy methods, which use bulk Soda Ash Sodium Carbonate and Calcium, then leave out elements, which often get used in conjunction at similar rates such as Magnesium and Strontium. This is still why I prefer the SeaChem or Complete Balling Method over the Economy dosing, Calcium Reactor, or Kalkwasser methods.

Here are a few key Minor/Trace Elements:


The marine aquarium has to have some basic chemistry understanding to maintain a successful tank. There are a handful of methods, which use different dosing methods, based on science and budget.
The most popular method used is different between different groups/nationalities of reef keepers. While there might be different successful ways to keep aquariums, with many examples, there are methods, which have been proven to be more successful than others, when looking at the details of the tank health.

What I personally find frustrating is not the different methods, often that involve understandable budgets; is rather the insistence by some, often by popular persons in social media that certain aspects are essential while ignoring aspects that would actually make more difference.

Case in point is the myth perpetuated by marketers and then picked by non discerning (or paid off) popular YouTube channels or other social media personalities that the use of DI water is essential for marine reef aquariums, all the while using inferior salt mixes or alkalinity and calcium maintenance methods.
All the addition of a DI chamber does for you is lower TDS somewhat compared to a good RO system and remove ions that would result in a residual higher pH (assuming the pH was high in the tap water).

Saltwater by nature is high in TDS and your tap water has to meet certain standards for toxins such as arsenic, so running a GOOD RO unit (not a cheap poorly made one) should lower your TDS enough to be sure there is nothing toxic of any consequence. Better to then spend your money on better slat mixes and better marine chemistry maintenance rather than doing this part "on the cheap" as many do while wasting their money on elaborate RO/DI systems after falling for the "cut and paste marketing".
Really about the ONLY time you would need this additional DI chamber is if you are on a well with very high nitrates (a good RO system still removes most nitrates) or you are running off from a home water softener unit.

Funny thing is, these same persons who will argue the use of getting every last TDS because they worry about 1 part in a billion of arsenic or similar are the same ones who have argued the use of why they should use a USDA approved silicone for their aquarium instead of a cheap unapproved hardware brand silicone.

Further Reading:
*Aquarium Silicone, Tank Repair, Applications, DIY, How To Use
*Use of RO, DI, Softwater in Aquariums

Keeping a reef tank as close as possible to natural ocean water conditions has always been the advanced marine keepers goal. With the addition of dosing a third part of trace minerals, which help keep an ionic balance, this really is the closest to natural sea water any aquarium keeper can keep. These minerals listed in this Reef Chemistry Article and the suggestions on how to maintain, really are the best current professional advice anyone can take and apply to their reef tank.

Other Recommended Reference & Product Sites


Reef Aquarium Care Basics
Saltwater Aquarium Information; Basic to Advanced

Aquarium or Pond UV Sterilization

AquaRay Ultra Premium Aquarium LED Lights


TMC Premium Fluidized Sand Bed Bio Filter
TMC Premium Fluidized Sand Bed Bio Filters


Ocean Nutrition Seaweed Salad
San Francisco Bay Brand Seaweed Salad



Hydor Smart Wave Controller
Hydor Smart Wave Controller


TMC Advanced Venturi Saltwater Protein Skimmers

TMC Advanced Venturi Saltwater Protein Skimmers


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In Chronological order of writing with the newest at the top

  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums


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