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You are here: Home Volume I September 2002 Feature Article: Jaubert's Method, The 'Monaco System,' Defined And Refined


By Julian Sprung Posted Sep 14, 2002 08:00 PM Pomacanthus Publications, Inc.
In this article I will focus on the simple method developed by Professor Jean Jaubert for establishing a reef aquarium.

Several methods or "disciplines" exist regarding the proper way to establish a living reef aquarium. While early developments feature the use of technology to purify the water with an assortment of external filter devices and fancy gadgets, other "natural" approaches rely mostly on biological filtration occurring within the aquarium. Natural systems of many kinds have been gaining in popularity over the last decade. As a result, the reef aquarium hobby has grown internationally, with systems that are successful, affordable and manageable for the average aquarist. Delbeek and Sprung (1994) gives a detailed account of the history and features of many of these systems. In this article I focus on one of them, the simple method developed by Professor Jean Jaubert for establishing a reef aquarium.

Part 1: The "Monaco System," Defined And Refined

Professor Jaubert is a coral reef researcher who works at the University of Nice, France and at the nearby Oceanographic Museum of Monaco. The public aquarium displays and the coral reef research facilities located in the museum utilize Jaubert's simple system. Since Jaubert's work is featured there, his system has come to be called the "Monaco System" by some aquarists. Others call it simply "Jaubert's method" or "Natural Nitrate Reduction" (NNR), the latter name coined by American aquarist/author Bob Goemans, who has written extensively about his own experiences with modified Jaubert systems. Jaubert's system was introduced to North American aquarists by Tom Frakes of Aquarium Systems, who visited Jaubert and reported what he saw in Monaco at the first MACNA, held in Toronto Canada.

The Museum in Monaco is located on the shore of the Mediterranean, and has a limitless supply of natural seawater on tap. The aquarium systems can be managed as "open system" aquariums, and many of the displays there are maintained via water exchange of 5% per day with Mediterranean seawater. Some are closed systems. A feature of most of the aquariums is prolific growth of corals, particularly of Stylophora pistillata, Pavona spp., Montipora spp., Galaxea fascicularis, and Acropora spp., but also many other species of stony and soft corals. Most of the corals there are from the Red Sea, but there are also some Caribbean gorgonians and some corals from Indonesia. Many of the exhibits are created entirely with corals grown "in house" at the Museum, not harvested from the wild. The aquariums also feature large populations of colorful reef fishes, including many butterfly and angelfish species not commonly maintained together with live corals in aquaria.


This aquarium using a deep layer of fine sand without a plenum shows an example of hydrogen sulfide development, the dark spot against the glass. Development of H2S pockets are more common in finer substrates, but can occur in any deep sand or gravel layer. The plenum seems to reduce their occurrence, however.

The system Jaubert uses is not magic, though its lack of devices might lead one to wonder how it could possibly be so simple. It relies on the ability of bacteria within the gravel to break down nitrogenous waste by aerobic nitrification and anaerobic denitrification. The process of nitrification is well known to aquarists, and is an important part of all successful aquariums. Bacteria convert ammonium waste produced by fishes into nitrite, and then nitrate. In the denitrification process the nitrate is broken down into nitrous oxide and nitrogen gas. These processes have been employed for many years in various filter devices for aquariums. In Jaubert's system, both nitrification and denitrification occur within a thick layer of gravel suspended over and in contact with a "void space" of water on the bottom of the aquarium.

The "void space" is called a plenum. The plenum space should be at least 1 cm in height and can be quite a bit taller. For most home aquariums a plenum space of about 2 to 3 cm is good. A support structure must be utilized to hold the weight of the gravel and any rocks placed over the plenum. The support can be as simple and inexpensive as the plastic plate from an undergravel filter, or it can be constructed by attaching plastic screening to a sheet of the inexpensive grid-like plastic light diffuser material "eggcrate," supported by cut lengths of PVC pipe (see photographs). In Monaco Jaubert uses thin rigid PVC sheets perforated with a grid of thousands of small holes, and cut lengths of PVC pipe for supports attached underneath. It is important to use an open structured material (ie. with many holes) that allows water to diffuse between the gravel layer and the plenum space, but does not allow the gravel to fall through the holes into the plenum.

The function of the plenum appears at first to be shrouded by a little bit of mystery.  It is the "magic" distinguishing feature of Jaubert's system. Many aquarists have stated or written that they believe the plenum serves no function. My experience contradicts their opinion, so I am stating for the record that Jaubert's system does work better for biological filtration than just putting gravel on the aquarium bottom without a plenum. I have also observed that the gravel placed over a plenum does not get as badly filled with detritus over time. Furthermore, systems heavily stocked with fish employing a plenum and thick gravel bed maintain significantly lower nitrate than aquariums without a plenum, using a gravel bed of the same thickness.

There is some explanation for this of course, so my testimonial is not simply in support of a mysterious phenomenon. The plenum provides a layer of water that maintains a level of dissolved oxygen above zero. Therefore the gravel in Jaubert's system is sandwiched between the highly oxygenated aquarium water circulating above it, and the plenum water, which maintains a low but generally stable level of dissolved oxygen. Being sandwiched between these oxygenated zones tends to prevent the formation of hydrogen sulfide, a common occurrence in deep sand beds without a plenum. Within the gravel bed above the plenum there are regions where the oxygen level approaches zero. That is where denitrification occurs. One might wonder what maintains the oxygen in the plenum space. Apparently it is produced by partial breakdown of nitrate (NO3), but it may be a byproduct of other reactions within the deeper layers of the gravel. These reactions involve the breakdown of organic matter, both dissolved and particulate, a food source for some of the bacteria that convert nitrate to nitrogen gas. The gravel does not become extremely dirty with accumulated detritus because the denitrifying bacteria utilize the detritus. Of course in any sand bed, worms, prototzoans, copepods, amphipods, and other creatures also help to maintain a healthy environment by feeding on detritus while gradually turning over the sand and gravel. There is a lot of life in the bottom substrate.

The gravel in Jaubert's systems has been termed "live sand," as it has in other natural systems such as Eng's and Dr. Adey's. The use of this term in connection with Jaubert's systems is misleading because the size of the grains used should be much coarser than sand. Other authors describing the installation of a plenum and "sand bed" have suggested layering different size grains of gravel and sand, starting with coarse on the bottom and becoming fine on the top. Since the sand bed does not function as a mechanical filter, and because it must allow good diffusion of water in order to function properly, the idea about layering makes no sense.  I do not make layers of different size sands, nor does Jaubert in his aquaria. The bottom substrate is composed of one type of coarse gravel only (grains mostly between 2 and 5 mm), not sand. Jaubert uses a screen more or less midway in the gravel between the plenum and the top of the gravel, to prevent diggers from disturbing the lower layer. It is possible to set up aquariums without any such screen by just leaving out the diggers (ie. gobies, pistol shrimps). If you want to have diggers you must use a screen, approximately 5 cm above the plenum. An alternative to placing a screen there is to use a couple of sheets of the black plastic geotextile material called Enkamat®. It has a structure that is tight enough to prevent diggers from disturbing the lower gravel layers and open enough to allow gravel to seep through. The gravel bed should be approximately 8-10 cm thick. The Jaubert system does not work well with a layer of gravel less than 8 cm thick over a plenum. If the gravel layer is too thin, denitrification is incomplete. As a result the nitrate level remains high in the aquarium, and there may be a chronic problem with nitrite as well. The same problem occurs if burrowing fish or invertebrates are allowed to excavate and reduce the amount of gravel covering the plenum.

Many aquarists believe the thick layer of gravel is a negative feature to the Jaubert system, from an aesthetic point of view. This aesthetic concern can be resolved by utilizing the Jaubert system with the thick gravel bed in an attached refugium aquarium. This way the display aquarium can be with no sand or a thin layer, whatever is aesthetically pleasing.

Aquariums with no plenum can achieve denitrification in a thinner layer of fine sand, but it is not as effective as a thicker layer of coarse gravel over a plenum, and the fine sand method has a higher risk of developing hydrogen sulfide gas (which kills fish rapidly). Author Ron Shimek is a proponent of the use of thick beds (25 cm or more) of fine sand without a plenum. He claims that such thick beds do not have a problem with hydrogen sulfide, and they function well for denitrification. I have not compared this method with Jaubert's.

Another distinguishing feature of Jaubert's aquariums is the paucity of live rock. Aquarists familiar with the "Berlin Method" are accustomed to seeing live rock filling 1/3 or more of the aquarium volume. In a properly established Jaubert system aquarium there is much less rock, leaving wide expanses of the bottom uncovered. The reason for this is twofold. First, since the biological filtration occurs within the gravel bed, the live rock is not needed for biological filtration. One can set up a Jaubert system with no rock at all. Its purpose is just for decoration and the introduction of biodiversity. The second reason for using very little live rock is that the surface of the gravel bed should be left uncovered as much as possible to allow unrestricted diffusion of water and oxygen.


The simple construction of a plenum using pvc pipe, eggcrate and screening.

Having less mass of rock in the aquarium offers some advantages. It offers more freedom of design for beautiful, natural-looking aquascapes. In fact, some of the aquascapes at the Oceanographic Museum in Monaco are the nicest I have ever seen in a public aquarium. Having less rock also means that there is less demand for calcium carbonate because calcium depositing coralline algae normally cover the surface of live rock.

With the introduction of Jaubert's method to the aquarium industry there has been a proliferation of erroneous claims and recommendations, some made by Jaubert himself, but most by other people who had little experience with the system. I thought it would be helpful to address these issues here, along with some observations of my own, now that I've had many years to test the system.

Protein skimming

Since the denitrifying bacteria need an organic food source, one might surmise that using a protein skimmer could result in a removal of too much of this food, to the detriment of the performance of the system for denitrification. It seems like a reasonable assumption, but in practice the use of protein skimming does not have any measurable effect on the denitrifying ability of a Jaubert system. Conversely though, it is my experience that the installation of a large surface area gravel bed over a plenum does in fact reduce the output of the protein skimmer. Therefore one can say that the gravel bed can biologically process much of what the protein skimmer removes. Nevertheless, protein skimmers are effective at removing phosphate from the water, an advantage that must be addressed in systems running without skimmers.


In a Jaubert system one may employ aeration, algae harvest, protein skimming, and or kalkwasser dosing to manage the phosphate level. The spontaneous precipitation of calcium phosphate in marine aquariums that are maintained at natural seawater pH helps to lower the dissolved phosphate level, given adequate supply of calcium. However, this process is easily overwhelmed with high inputs of phosphate from the makeup water or from the food added for a large population of fish. In addition, dissolved organically bound phosphate can persist in the water, and particulate organic phosphate accumulates in the substrate. As I mentioned, protein skimming helps to remove dissolved phosphate. The bubbling action of airstones can also lower the dissolved phosphate level in the water by ejecting phosphate as an aerosol (see Spotte). Dosing the aquarium with kalkwasser (calcium hydroxide solution) causes rapid precipitation of dissolved phosphate due to the supply of calcium ions and the increase in pH caused by the hydroxide ions. The precipitated phosphate is insoluble at natural seawater pH, so while it accumulates in the aquarium in the bottom substrate, it is generally not available to the water column. Algae growing on the substrate may be able to obtain the phosphate by secreting special enzymes that digest it. Algae may also employ the activities of symbiotic bacteria that secrete enzymes to liberate phosphate bound to the gravel or tied up in organic detritus. Harvesting and removing algae such as Caulerpa spp. from the aquarium is a way to export phosphate. Particulate phosphate (organic and inorganic) can also be exported via protein skimming, and siphoning to remove it during water changes.


As in any strongly illuminated aquarium, the management of algae creates a need for herbivores, so Jaubert's system is no exception in this regard. However, one noticeable difference in these systems is that a properly functioning gravel bed of sufficient size will dramatically reduce the growth of algae on the windows of the aquarium. For the management of cyanobacteria "slime algae" and filamentous algae I recommend small hermit crabs, various herbivorous snails such as Atraea, Lithopoma, Turbo, Trochus, Nerita, and Cerithium, and the sea urchin Diadema setosum. Surgeonfishes or Tangs and other herbivorous fishes may also be employed for algae control. The bacteria in a healthy gravel bed are capable of breaking down nitrogenous waste so quickly as to be able to limit the growth of algae (and corals- I'll say more on that in a moment). Initially, however, all of my Jaubert systems show a prolific growth of macroalgae lasting approximately six months. Thereafter the algae growth slows down or stops completely unless I feed the aquarium heavily enough to increase its growth.

Yellow Water

Yellowing of the water in closed system aquariums is an inevitable effect due to the accumulation of dissolved large organic compounds. While it is true that some dissolved organic compounds are broken down by the processes in the gravel bed in Jaubert's system, this does not mean that the processes prevent the water from turning yellow. Jaubert's systems may not become yellow as quickly or as severely as other natural system aquariums, but they do become yellow. Activated carbon effectively removes water-tinting dissolved organic matter.


An exhibit at the aquarium in Monaco featuring a Red Sea Regal angel, Lionfish, a large bubble coral, and the soft coral Sinularia.


Many of the closed system aquariums I saw in Monaco utilized aeration for water motion. The benefits include the aforementioned removal of phosphate, no heat transfer to the water, low electrical power consumption, and plankton- friendliness. The disadvantage of aeration is salt spray formation, which produces salt creep and corrosion of materials near the aquarium. I discovered a potential problem with Jaubert systems that is solved by aeration. If the aquarium does not employ a surface-skimming overflow, the night-time oxygen level may fall to extremely low levels, which is stressful or even fatal to fishes. It is likely that a low oxygen level at night also promotes the release of hydrogen sulfide from the gravel, which would suffocate the fishes. A surface skimming overflow insures sufficient gas exchange to keep the oxygen from falling too low, and rapidly causes an off-gassing of any hydrogen sulfide. It has been my experience that in the absence of a surface-skimming overflow it is necessary to include an airstone or bubbler to keep the oxygen level up at night and quickly dissipate any hydrogen sulfide that might be released into the water.

Calcium And Trace Element Maintenance

Jaubert originally promoted the idea that the aragonite gravel in his systems dissolves, and that this dissolution supplies the calcium and alkalinity needed for coral growth. Deep within the gravel bed the pH is low, and this effect does dissolve the gravel, liberating some calcium and carbonate to the water. In aquariums with strong illumination and strong coral growth the quantity of calcium carbonate released is not sufficient to keep up with the demand. Jaubert later observed (personal communication) that the addition of "kalkwasser" or other means of calcium and alkalinity maintenance must be employed to maintain the calcium and alkalinity for his closed system aquariums when they have large coral populations.

Some authors have suggested that the dissolving substrate provides an ample supply of all necessary trace elements. This is simply not true. It is true that dissolving gravel supplies some strontium, magnesium, and other minerals such as iron, but not sufficiently to meet the requirements of the growing corals, and there are other elements such as iodine that are not supplied by dissolving of the gravel. One must remember that the food added to the aquarium is an important source of trace elements, and water change may also bring in a supply of a few trace elements in excess of natural seawater values. While some trace elements may actually accumulate over time in closed re-circulating aquariums, some are nevertheless depleted from the water rapidly and need to be supplemented.


Illumination of a Jaubert system aquarium is not different from what is used for any other reef aquarium system. The effect of the light is important as it relates to the effect photosynthesis has on the oxygen and pH of the body of water above the gravel. Jaubert's patent refers to this effect, comparing the high dissolved oxygen and high pH in the aquarium water with the low dissolved oxygen and low pH of the water in the gravel and plenum. This potential difference caused by the effect of the light may assist the diffusion of water and dissolved substances through the gravel.

Gravel Turning Into Rock

Some aquarists have reported a problem with gravel fusing into a solid mass of rock. This occurrence of course can to some degree prevent the proper functioning of the gravel bed as a biological filter, though if the mass is still porous it might not be so problematic. I have not personally experienced this problem, and believe it is caused by very high alkalinity levels combined with certain types of aragonite gravel, oolitic sand in particular. Larger gravel size should prevent this problem for the most part, though I have heard reports of it affecting aquariums using even coarse gravel. The problem is not common, and until the exact environmental causes are described, I cannot offer definitive advice on how to prevent it.

Plenum Water

Some authors have suggested that the plenum water accumulates nutrients and therefore needs to be changed periodically. Jaubert never made this claim. My practical experience with his system, including measurement of nitrate and phosphate levels from plenum water samples, convinces me that the system is dynamic, and so the plenum water is not a nutrient sink.  At times nutrient levels rise, but they also fall again, so they do not accumulate. It is true that nitrate and nitrite may be found in the plenum water at levels much higher than in the water above the gravel. Sometimes phosphate and silicate levels are elevated in the plenum as well (J. C. Delbeek, personal communication). However, the levels do not stay high, and the plenum water does not cause sudden fluctuations in the water quality of the aquarium, as has been suggested by some authors. An exception can be when a burrowing fish or shrimp moves away enough gravel to expose the plenum water. That could cause a sudden nutrient influx into the tank and a resulting strong growth of algae. The second screen layer I described earlier prevents such burrowing from exposing the plenum.

Part Two: Techniques for setting up a Monaco System

In the first part of this article I described the distinguishing features of a Jaubert or Monaco style aquarium. In the second half of the article I describe how to set up an aquarium using this method, including a few variations on the theme. I also show how you can add the system to an existing aquarium.

Set Up Techniques: Standard Monaco System


A free-standing aquarium in Monaco. This one did not have continuous water exchange.

The "standard" Monaco system aquarium is very easy and inexpensive to install. All one needs are the aquarium, cover lid, lights, the plenum, screen, gravel, an air pump, air tubing and air diffusers. The water motion is accomplished by means of the air diffusers. Additional water flow can be accomplished with submersible water pumps or by plumbing in line water circulation pumps. In any case, when using the "standard" Monaco system there should be at least one air diffuser, which can be operated at night by means of a timer. In my experience the aeration helps to prevent sudden losses of fish due to a sharp drop in the oxygen level at night. During the day, photosynthesis by plants elevates the level of dissolved oxygen in the water above saturation. At night the lack of photosynthesis by plants (because there is no light) causes a large drop in the dissolved oxygen. This is especially pronounced in a Standard Monaco System because the enormous population of bacteria and microorganisms in the "live sand" bottom within the aquarium consume oxygen. It is also possible that at times some hydrogen sulfide is produced within the gravel, and it may enter the water column, especially at night. During the day, the elevated oxygen concentration in the water circulating above the gravel bed penetrates the gravel and thus keeps the low oxygen layer (and any hydrogen sulfide, if present) within the interstitial water of the gravel bed deep below its surface. At night because of the drop in oxygen level in the water above the gravel due to respiration by plants, fishes and other creatures, the lowest dissolved oxygen level within the interstitial water in the gravel bed approaches the top of the bed. If there is hydrogen sulfide gas within the gravel bed it may be released at night, which is the worst possible time for the sake of the fish. Hydrogen sulfide is a poison that rapidly depletes oxygen from the water and suffocates fish. Release of hydrogen sulfide from the gravel at night may occur occasionally. It only becomes problematic for the fish if there is not sufficient agitation of the water surface and aeration, which "blow" the hydrogen sulfide gas from the water and elevate dissolved oxygen. Normally there is little if any hydrogen sulfide production in a Monaco system, and low oxygen concentration alone is the night-time threat, the same as it is in any reef aquarium system that has a high density of life in a small volume of water.

I encountered this problem in my initial experiments with Jaubert's system, and it was not corrected by simply increasing water circulation with water pumps. The addition of a protein skimmer did not solve the problem either. The surface breaking affect of the aeration was needed. I have been able to achieve the same benefit as air diffusers by using an appropriately sized submersible water pump placed on the bottom of the aquarium to send water directly upward to the surface, creating a "boiling" effect like a natural spring. However, as the pump becomes clogged over time, and the output is reduced, the surface agitation subsequently becomes reduced, which increases the risk of a lethal low oxygen level at night. As an alternative, one could plumb a pump in-line with a removable mechanical filter on the intake to achieve the same effect see drawing. One more thing that became clear to me in my initial experiments with the Standard Monaco system was that fine sand tended to produce lower oxygen levels at night compared to coarse gravel. This is one of the reasons for using coarse gravel instead of sand.

Monaco System With Surface Skimming Overflow

The use of a surface skimming overflow in the design of a Monaco system eliminates the problem with low night-time oxygen level. The constant renewal of the water surface plus the cascading of water over the overflow and down the drain pipe effectively oxygenates the water. In my opinion this is the best way to set up a Monaco system for most reef aquarium applications. The only problem with surface skimming overflow designs is that anemones, nudibranchs, shrimps, sea cucumbers, or other delicate creatures might wander over the overflow or get damaged by being drawn into the overflow's strainer grid.  I have devised a modified system for these creatures, as I'll shortly describe.

Monaco System As An Attached Refugium

The use of Jaubert's method in an attached "refugium" is a simple way to "upgrade" any existing Berlin system aquarium to make use of the nitrate lowering ability of a plenum system. A separate aquarium is set up with a surface skimming overflow and plenum. Water from the main display is pumped to the refugium and it drains from the refugium back to the display aquarium or back to the sump from the display aquarium. It is also possible to make the refugium work as part of the sump, having water drain to it from the display tank. In this case the refugium should drain to a second sump from a pump sends water back to the display tank (see diagrams). When the Jaubert system is employed in an attached refugium aquarium, the photoperiod can be set to be opposite that of the main display aquarium. Such "reverse daylight' systems offer advantages in the balance of oxygen and carbon dioxide production in the system, and thus help to balance the swings in dissolved oxygen and pH from day to night (see Adey and Loveland, 1991).

Modified Technique - Hybrid With Undergravel Filter

I thought of a new way to employ Jaubert's system in an aquarium without a surface-skimming overflow. The design allowed strong water motion without the risk of damaging mobile soft-bodied creatures such as sea anemones and nudibranchs. What I did was to put a small undergravel filter plate with lift tubes under the gravel at one end of the aquarium only. In a long aquarium this plate typically covers about 1/4 or less of the tank bottom. The rest of the tank bottom is covered by a plenum, which can be made with an undergravel plate too, but without the lift tubes. In practice my modification had some positive aspects but also several negative ones. It did eliminate the problem of losing anemones or nudibranchs to a suction intake or overflow drain. It also had the ability to mechanically filter and thus rapidly clarify the water. On the down side it did not effectively lower nitrate. On the contrary, the nitrate level increased over time, apparently because the aerobic bacteria in the undergravel filter portion of the aquarium substrate produced nitrate more quickly than it could be broken down in the rest of the substrate. Another problem was that airlifts produced a raft of bubbles on the water surface that reduced light input. To resolve this latter issue I tried using a water pump instead of airlift to circulate water through the undergravel filter, and the result was an even more rapid accumulation of nitrate.

I tried a modified overflow design to deal with the potential for losing small shrimps and seaslugs such as Elysia. Instead of using an overflow box, I simply drilled a drain hole in the back of the tank and inserted a bulkhead fitting and strainer. The strainer has to be cleaned about once every few weeks, but it is easy to do and this technique is safe for shrimps and seaslugs. There is always a risk of an anemone wandering into such an overflow and plugging it up.

Setting up a Jaubert System

Fill the aquarium with saltwater to a height of about 8 cm. Then put the plenum support structure down, making sure to shake out any trapped air bubbles. If this support structure is an undergravel filter plate, put the plate directly on the bottom. The space underneath it is sufficient as a plenum. Be sure to cap off the lift tube holes. After rinsing the gravel a few times in a bucket with tap water, put the first layer down on top of the plate. Add the gravel until you have made a layer approximately 5 cm thick. Next put a layer of plastic window screen, cut to fit the inside dimension of the aquarium, on top of the gravel. This will prevent burrowing organisms from disturbing the lower gravel layer. Next add another 5 cm of gravel on top. It is possible to add live gravel from another aquarium on top. Then put a dinner plate on top in the middle of the tank and pour the rest of the saltwater in over the plate (which prevents the water from stirring up the gravel as you pour. In the first part of this article I mentioned the use of Enkamat geotextile material for preventing burrowing animals from disturbing the lower gravel layer. If that material is used, it is to be placed directly on the plenum support in layers to a thickness of approximately 5 cm. The first layer of gravel is added on top of the Enkamat, and the gravel simply sorts through it to fill the spaces between the Enkamat filaments (see photo). Once the water is added the circulation pumps should be started. Lighting should be provided as usual for a photoperiod of approximately 12 hours.

Adding Rock To A Jaubert System

In the first part of this article I explained that Jaubert systems do not need and should not have a large amount of live rock in them. The biological filtration is accomplished by the gravel, so the rock is used for aesthetic purposes and for introducing biodiversity (many species of algae, microorganisms, and invertebrates).

In the simplest approach, one may add one or two large rocks to the aquarium, placing them on top of the gravel. The less one covers the gravel the better because the system operates by diffusion of water and dissolved gasses across the gravel surface. The corals and other invertebrates can be placed on or attached to these rocks. One may altogether forego adding rocks to the aquarium, using just live corals for the decoration.

If the aquarium is large it is wise to plan the aquascape in advance, and it is possible to begin constructing it when the aquarium is dry. The rocks used can be dry porous limestone or dead coral skeletons. Lightweight pieces may be cemented to the walls of the aquarium while still dry using a suitable non- toxic epoxy. A large open-design rock structure can also be constructed dry within the aquarium using hydraulic cement to hold the rocks together. Jaubert and his team have designed and built some of the most magnificent displays this way. After the aquarium is filled with water, one may add a few pieces of live rock to "seed" the system with coralline algae, and live corals can be attached to the dead rock and walls of the aquarium with underwater epoxy.

Part 3 Maintaining a Monaco System Aquarium

Harvesting algae

In part one I explained that my Monaco systems exhibited strong algae growth in the first six months. This needed to be harvested once a week initially, then less afterwards. When a protein skimmer is employed on a Monaco system the growth of algae is much reduced. Also the use of herbivores such as Diadema setosum is effective in limiting the growth of various algae, but they can only be employed in large aquariums. Small hermit crabs are effective for tiny aquariums.

Water change

During the first three or four months I do not change water, but rely on the harvest of algae to remove excess nutrients, as I described in part one of the article. Once the algae growth begins to slow down I may start water changes of five or ten percent per month. In many cases I have set up these aquariums with no water change at all (for several years). If no water changes are done, it is especially crucial to monitor salinity, calcium and alkalinity, as well as supplement calcium, trace elements, and alkalinity. Salinity drift can be managed with automatic water top off to replenish evaporation and the occasional addition of some saltwater to replace salts lost due to spray and protein skimming (if one is used).

Supplements And Feeding

I add trace elements weekly, including iodine and also add strontium. I add food daily.  I feed the fishes a variety of foods including mysis shrimp, live worms, dry pellet and flake foods, and dried seaweeds. For filter feeding invertebrates I add MarineSnow ™ daily.

Initially the biological filtration in a newly set up Monaco system does not have the capacity to process large food inputs, even when some live sand was added. It takes several months for the system to mature. As I explained in part one, the decrease in algae growth is an indicator of maturation. Measuring the decline of nitrate is another means of checking the system's capacity.


Jean Jaubert cleaning the viewing window of one of the coral culture aquariums in a lab behind the scenes.

Calcium And Alkalinity Maintenance

I use two methods of calcium and alkalinity maintenance. The primary one is kalkwasser (calcium hydroxide in water) addition for top-off of evaporation. This method is described in Delbeek and Sprung (1994). The secondary calcium and alkalinity maintenance system I use is the two-part calcium and alkalinity product called C-Balance. C-Balance is especially helpful for maintaining calcium and alkalinity in aquariums with low evaporation rates combined with a high population of corals. A third possibility for maintaining calcium and alkalinity is the use of a calcium reactor in which calcium carbonate gravel is dissolved by carbon dioxide gas. I have not tried that method on a Monaco system aquarium, but I believe it would work just fine. One of the aquariums shown in part one of the article, photographed in Sao Paulo Brazil, utilizes a calcium reactor quite successfully.

While it's best and less time consuming than manual additions to utilize a dosing pump for the daily addition of kalkwasser, I have devised a simple manual approach to kalkwasser additions that I employ it in some of my Monaco style aquariums. I have determined that it is safe to add, all at once, the following dose per 150 litres of aquarium water:

  • 1 ml (= 1/4 teaspoon) of dry calcium hydroxide powder, mixed first in a container of water (about 500 to 750 ml of water is sufficient).

Be careful not to exceed 1ml calcium hydroxide per 150 liters of aquarium water! Overdose of kalkwasser raises the pH too high and can kill fish and invertebrates.

I add this quantity to some of my aquariums in the early morning hours when the pH is naturally lower in the aquarium. Of course I pour the mixture slowly into a strong current stream to avoid concentrating the high pH kalkwasser over any of the invertebrates.

Another dose may be added several hours later, not sooner.

One can plan to add kalkwasser this way in the morning and then again at night. If the amount of water needed exceeds the evaporation rate, one can simply use some of the aquarium's water in the mixing container.

Cleaning The Gravel

I do not stir and clean the gravel in my Monaco system aquariums. I do employ some animals that help keep the gravel surface clean, and other animals that keep the glass adjacent to the gravel clean. As I explained in part one of the article, in my experience the gravel in these systems does not become overly clogged with detritus. It seems that the denitrification process helps to break down some of the detritus, so that heavy accumulations are rare. Various worms and other creatures in the gravel also eat the detritus.

For cleaning the gravel surface, sea cucumbers are particularly effective, as are small Conchs (_Strombus_ spp.), small hermit crabs, and serpent starfish. Small snails of the genus Stomatella (see Delbeek and Sprung, 1994) often reproduce on the rocks and in the gravel, and they are good herbivores. One should not utilize sand sifters that actively dig deeply, such as various sifting gobies, unless a screen is installed to prevent them from digging too deeply (see part one of the article).

I found that several species of Chiton that commonly live on the undersides of live rock are particularly effective at cleaning the glass adjacent to the gravel. They actually burrow through the gravel while attached to the glass, feeding on algae growing there.

Airstone Maintenance

If airstones are used for water circulation, they must be cleaned or replaced periodically to insure the adequate flow of air. Sometimes salt or minerals build up inside the airline tube, and this must be cleared periodically. When aeration is used it may lead to accumulation of salt deposits around the aquarium perimeter. This "salt creep" must never be allowed to accumulate on electrical apparatus and it must not be allowed to fall back into the aquarium where it could land on and injure sessile invertebrates.

Temperature Maintenance

As with any reef aquarium, it is important to maintain the temperature stable and ideally below 80 degrees F. This is because of the relationship between temperature and dissolved oxygen in the water. At higher temperatures less oxygen is held in the water. This problem is enhanced by the thick gravel bed and associated bacteria and fauna in a Monaco system. The abundant life there consumes a lot of oxygen. Be sure to maintain the temperature cooler by using a chiller, air conditioner, or evaporation. Keep it stable with a heater in the winter time. Stability of temperature and dissolved oxygen level are important factors in maintaining healthy fishes. Low oxygen and temperature fluctuations tend to promote the incidence of fish diseases, especially Cryptocaryon and Amyloodinium.


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  4. Jaubert, J. and J.P. Gatusso, 1989. An Integrated nitrifying-denitrifying biological system capable of purifying seawater in a closed circuit system. In Deuxieme Congres International d'Aquariologie (1988) Monaco. Bulletin de l'Institut Oceanographique, Monaco, No. special 5:101-106.
  5. Jaubert, J. 1991. United States Patent number 4,995,980
  6. Jaubert, J., Pecheux, J-F., Guschemann, N., and F. Doumenge. 1992_. Productivity and calcification in a coral reef mesocosm_. In Proceedings of the 7th International Coral Reef Symposium.
  7. Spotte, S. 1992, Captive Seawater Fishes: Science and Technology. John Wiley and Sons, Inc. New York. 942 pp.
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