Long-Term Considerations for a Successful Reef Tank

A lot of aquarists tell me that the most exciting part of a reef is setting it up and stocking the tank. For others, the excitement comes from watching the reef develop and change over time. A reef tank is certainly a long-term commitment. I often remember reading German articles, where they would describe a one year-old reef as a new system. There are certainly a lot of things that change within a reef aquarium over time. And what I'm discovering is that the habits and practices of the reef keeper have to change over time as well. This article is intended to address long-term concerns, and suggest steps a reefkeeper should consider taking with a reef aquarium that he/she intends to keep for many years.

Keep the Variety and Number of Corals Low

Many of the choices a reefkeeper makes when designing a new reef will determine the long-term health of the system. People spend a lot of time and energy planning the plumbing, lighting, and filtration. The Reef Central forums are often filled with hundreds of questions concerning what wattage lighting to purchase or which skimmer is best. Unfortunately, little thought or research is put into stocking the reef. The most detailed planning one may find concerning livestock may be that a reefkeeper has decided to do an "SPS" reef or a lagoon.

Once the reef aquarium is up and running, it usually gets quickly filled with corals. Corals are placed in close proximity to each other, without regard to growing room or competition. Reefkeepers tend to plan their reef on how they would like it to look immediately or how they foresee it a few months from now. They do not plan their purchases by what the reef will look like in several years. I'm certainly guilty of this; it is hard to resist buying yet another coral at the local fish store. But, the reality is that corals will grow and compete. And some of the negative effects of this competition and growth will not be manifested for years.

Look at the density of the corals on natural reefs pictured in dive magazines or in sources like National Geographic. One will see that there is very little "real estate" available. But, also look at the diversity. One will notice many similar or same types and/or species of coral growing together. Now, compare such a picture to a reef tank. One will see that we are bunching way too many corals of different varieties into too small of a space. The problem with this kind of crowding is that there is going to be more interspecific competition between corals in the reef tank as a result. Competition is a source of stress, and eventually, some corals are going to be out-competed by others. Byproducts of chemical competition may also do more harm in an aquarium compared to a natural reef because it is a small, closed body of water. Such chemical byproducts could build up in the system over time.

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A gorgonian-dominated sand flat in the Florida Keys.

By reducing competition, the reef aquarium is going to be much healthier in the long term. Over time, stronger competitors will always win out over those that are not as competitive. If one were to stock a tank full of coral species, and then not add any more for the life of the tank, eventually, only a few would remain. It may take years, but it will happen. The reality is that most reefkeepers will keep adding more corals to replace those that have been lost. This perpetuates the problem, and will ultimately be the cause for more losses. Pruning certainly helps prevent a lot of direct competition from occurring, but I think pruning should be complimentary to low stocking levels. The same can be said for other preventative measures, like using carbon and water changes to dilute the byproducts of chemical competition.

When planning an ideal and natural reef, one should consider keeping the diversity of corals to a minimum. Intraspecific competition is easier to deal with than interspecific competition. The problem is, nobody wants a tank full of the same corals. It's more enjoyable to buy a new and different type of coral. That's what makes visiting the LFS so much fun! It is the desire to find something new and unique!

But, a tank can still be very beautiful with a lower variety of species. At the Ft. Lauderdale MACNA convention, Julian Sprung displayed some striking photographs of reef aquariums around the world. One notable aquarium consisted of a single large Acropora colony filling a cube-shaped tank. The tank also contained many small damsels that hid among the coral's branches. It was inspiring. I also see a lot of reefkeepers reach a point where they strive for their reef to be more natural, or perhaps geographically specific. Hopefully, such trends will become more popular to help alleviate a constant desire to add something new and different. Another benefit to a more natural tank with lower coral diversity is that it will also offer more natural behaviors and trends to observe.

An analogy with fish stocking levels provides further support for my argument here. Coral reefs are teeming with fish. The unwitting aquarist may use this observation to justify overstocking a tank with fish. The correct response to this action is that the ocean contains a much larger volume of water and more ways to process nutrients than a small glass box full of water. I suggest approaching coral stocking levels the same way. I certainly haven't always practiced what I've preached. My previous reef tanks have been stocked to the brim with corals of many different types. But, I certainly intend to plan future reef aquariums accordingly. I think it will be much more rewarding to have fewer, but larger, corals than to have many small "bonsai" corals that I must prune frequently.

Monitor and Adjust Current and Light in a Reef Aquarium Over Time

Adequate light and good water flow are vital to a healthy reef aquarium. As the quality of light and current change, so does the health of the reef aquarium. It is important to replace lamps regularly. It is generally well known that lamps will diminish in intensity as they age. Pumps and powerheads will also produce less current as the tubing and impellors become restricted with the build-up of fouling material. It is recommended to clean pumps and tubing/PVC regularly. Several years of buildup can make a significant impact on flow.

Another factor that causes changes in light intensity and current is the very thing one strives for...coral growth! As corals grow, they block areas of water flow. For example, envision a small coral fragment mounted near a powerhead. As this fragment develops into a large colony, it may block the current generated by the powerhead, preventing it from reaching other corals. As a coral grows larger, it may also begin to shade corals below it. Sometimes, an aquarist will be perplexed as to why a coral that has been thriving for years suddenly begins to fade away and die. He/she notes that none of the neighboring corals or fish seem to irritate it, and that the water quality is high. But, perhaps other things have changed. Perhaps a neighboring coral has grown considerably and eventually reduced the flow or light reaching the now ailing coral. I have found that certain small-polyped stony corals, such as Acropora, are particularly sensitive to this. Overtopping and flow restriction are indeed another type of competition.

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Notice the table coral beginning to shade the real estate below it.

As the reef continues to grow, it is worth repeating the importance of keeping light and current optimal. An easy solution is to add more light and more pumps/powerheads to accommodate the growth. Repositioning them will help as well. Pruning heavy growth will help prevent shading and reduced water flow. Lower coral stocking densities also helps in this regard.

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Rapidly growing corals, such as this Acropora yongei, may impede water current in the tank over time.

Maintain Biodiversity

The more biodiverse an ecosystem is, the more stable it is. As species go extinct, not only is that organism lost forever, but it contributes to the destabilization of the ecosystem it inhabited. All organisms fulfill a role or "niche" in an environment. In a sense, they all work together to make the system work. The same principles apply to an aquarium. One way diversity increases stability is by increasing the complexity of the food webs and nutrient pathways. As aquarists rely more and more on natural forms of filtration such as deep sand beds, live rock, and macroalgae-filled refugiums, they are beginning to understand the importance of biodiversity.

I can remember a time when bristle worms were the bane of every reef keeper's existence. Now, we admire them fondly as "detritivores." A deep sand bed would not function properly without the presence of various detritivores to break down large organic particles in order to make this material available to bacteria and smaller organisms. Other fauna contribute by breaking up bacterial clumps and inorganic material. There are also "critters" that contribute to the health of the tank by grazing on algae or perhaps acting as a food source for corals and fish. Unfortunately, many of these critters eventually dwindle and disappear from the tank over time. Predation from fish and corals, competition from other critters, and random catastrophic events (like a wild temperature swing from a failing air conditioner) all contribute to the disappearance of these beneficial critters from the reef aquarium. There are many steps an aquarist can make to alleviate this loss of diversity.

One popular method to increase biodiversity is to add a refugium. By definition, a refugium is an area where organisms are allowed to thrive without the presence of predators. This could be a separate tank or even a section of the sump. Today, manufacturers are making hang-on-the-back refugium units for aquariums. A refugium may alleviate the predation problem for the organisms found there, but what about the competition and random catastrophic events?

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Refugiums such as the one above are relatively simple to add on to existing systems, and are an effective way to maintain faunal biodiversity in a reef aquarium.

In natural ecosystems, there is immigration and emigration. Many organisms will move from one area to another. If something catastrophic occurs and destroys a whole population of trees or birds in a given habitat, neighboring communities can help recolonize the area. In a reef tank, this does not occur. Despite having a refugium to mimic some of this recolonization, a reef tank is still a closed system. Consider a tank as a very remote island. It is isolated. If a particular population of organisms is eliminated from the tank and refugium, there is no way for that type of organism to recolonize the tank...unless the reefkeeper steps in.

I personally think it is good practice to play Mother Nature from time to time and restock the tank with micro- and meiofauna. Many online stores carry detritivore "kits," which would allow one to re-establish some of these critters in a reef aquarium. Another way is to replace a couple of pieces of old live rock with fresh (cured) rock. The new live rock can aid in reintroducing some of the lost populations. Unfortunately, there is also a risk of reintroducing nuisance organisms, but I think the benefits far outweigh the risks.

Choosing fish wisely is another good way to maintain diversity. Reducing the amount of predatory fish will certainly help. Feeding more heavily and providing a variety of food types and sizes will contribute to sustaining a diverse reef, by meeting the nutrient demands of more organisms. Support of this suggestion is found in the various comments I hear from aquarists that begin feeding plankton substitutes. They notice an increase in many organisms, from sponges to microfauna.

Perhaps the reader may feel that the suggestion of maintaining biodiversity conflicts with the suggestion of keeping less corals, but many corals tend to fill the same or similar niches. By maintaining diversity, I refer to the goal of filling and maintaining a large variety of niches.

Simulate Storms

Detritus builds up in areas of the tank despite our efforts to maintain large populations of detritivores, strong current, and proper filtration. In a closed reef aquarium, it may even become a problem. Some suggest that long-term accumulation of detritus can lead to mysterious algae problems. Others suggest that detritus can also clog the porous live rock in our system, reducing the surface area on which bacteria, sponges, and other filter feeders settle. I'm not entirely sure if these concerns are legitimate, but I personally think it is beneficial to occasionally simulate the action of storms with large powerheads and other devices to remove detritus build-up. I also try to occasionally manage stagnant areas with a turkey baster when doing water changes. Stirring up the detritus is also a good way to feed your corals. I would, however, recommend only disturbing small pockets of detritus. Disturbing large sinks of detritus, such as stirring a deep sand bed, can have catastrophic effects on the tank. Releasing large amounts of detritus will also release large densities of aerobic bacteria and microbes into the water column. These organisms may use up a lot of the free oxygen in the water column thereby reducing the overall oxygen levels in the tank. The freeing of large amounts of organic material may also cause an algae bloom down the road.

Water Changes

The importance of water changes is obvious. In aquariums housing only fish, water changes are often implemented to dilute the buildup of nitrogenous waste. However, they act to dilute other things in a reef aquarium. Other detrimental elements originating from food, impurities in top-off water, and other inputs can accumulate if not removed. Water changes will dilute these elements, as well as the possible products of plant and animal metabolisms, such as the toxic chemicals released by soft corals. Water changes also replenish elements not provided by additives and food. It should be little wonder why corals tend to perk up after a water change.


A detailed logbook becomes an asset of information over time. Events that occur in a reef tank are not always a result of recent changes. They could be a result of something the reefkeeper did a long time ago. For example, changes in feeding, additives, or frequency of water changes may not cause any immediate effects in an aquarium. It may take months or even longer for the effects of such changes to show. A detailed log is a useful tool in helping to solve these mysterious changes that may occur over time. By logging quantities of items added to the tank, changes to lighting and temperature, and other notable information, one suddenly finds variables that might be able to explain current happenings.


These are just a few suggestions to help keep a reef aquarium thriving for many years to come. But, be aware that a reef will evolve and change. As years pass, one may suddenly discover that a tank will no longer support certain corals, no matter how many times the reefkeeper attempts to reintroduce them. The tank is not necessarily going to evolve the way an aquarist wants it to. But, that does not make the system a failure. It's important for an aquarist to evolve, as well, and learn the limitations of his/her reef. I also think it's important that those who have successfully kept reef aquariums over long periods of time submit their ideas and methodologies that they believe contributed to their success (or failure). I would like to hear from you!!

If you have any questions about this article, please visit my author forum on Reef Central.

Useful Links:

Reef Aquariums: Coral Compatibility by Charles Delbeek


I would like to thank Steve Chang for allowing me to photograph his wonderful tank that is used in some of the pictorial examples above.

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Long-Term Considerations for a Successful Reef Tank by Mark van der Wal - Reefkeeping.com