The “Old Tank” Syndrome

by | May 15, 2006 | 1 comment


Over time, big stag horn Acroporas and other large corals will eventually slow the flow of water throughout the tank

The success that reef keepers have achieved in the last ten to fifteen years has been nothing short of spectacular. It is now possible to keep many of the fish and corals that only a short time ago were thought to be impossible to keep. This process has required us to learn many things that previously we had not even thought about. In the early days of the saltwater hobby before the nitrogen and other cycles were fully understood, many hobbyists had to suffer from what was called “new tank syndrome.” This usually occurred soon after a tank was set up and a few fish were added and then for some unknown reason they all would perish. Fortunately once the nitrogen cycle was understood and the need for developing a bacterial filter common practice, this syndrome was no longer a problem. Now that a tank no longer needs to be broken down and tanks are being maintained for long periods of time a new “syndrome” is starting to show itself. For lack of a better term the situation is being called the “Old Tank Syndrome.” This syndrome is not as dramatic as the new tank syndrome where all of the fish died, but it can be just as unsettling to the tank’s owner.

The best way to describe this syndrome is simply that the tank is failing to thrive. For those of that have had reef tanks for an extended period of time we know when looking at a tank whether it is thriving or whether it is simply holding its own or failing. In the case of a tank that is going through old tank syndrome it is starting to decline. This situation usually occurs after a tank has been set up for five years or longer, although it can occur earlier. The syndrome is usually the result of a number of factors working together to cause the demise of the tank, although a single factor if it is great enough can also lead to the problem. In this article I will address each of the possibilities for its cause individually as well as their possible solutions, in the hope of helping those who have a tank suffering from it to bring it around.


Algae will even grow in the outflows when the nutrient levels are high as it is difficult for herbivores to reach these areas.


Benign Neglect

The single biggest cause for a tank to suffer this syndrome is actually the result of its success. As a tank ages and the corals and fish thrive and grow a number of things start to happen. Fewer new additions are made to the tank due to space limitations and as a result the excitement that occurs when a new fish or coral is added no longer occurs. (As a side note we need to admit that this hobby is very addicting and adding something new is kind of like a fix for us that gets us all excited again and keeps us motivated to keep the tank at an optimum level). In addition, this success leads to the feeling that what we are doing is working, so we do not need to change or improve upon our techniques even as the tank is changing itself. A saltwater aquarium is not a static entity, it is a fluid one, no pun intended, and therefore we need to constantly tinker with the system to keep it at an optimum level.

This not changing what we are doing is not the major cause of why a tank is no longer thriving, it is more of a result of our getting a little lazy and taking for granted that we have become experts at managing the tank. As a result, we tend not to do the tedious things necessary to keep a tank at its optimal level or if we do them we do not do them with the same frequency that we did when the tank was thriving. After observing several hundred successful tanks it has become apparent that the tanks that continued to thrive over the long term were the ones where the owner continued to take meticulous care of them. They did not cut corners or reduce their level or frequency of care despite the tank doing well. That is why I placed this section first, in that even if some of the later topics occur, as long as neglect of the tank does not take place the tank will still probably do well.



A large fish population can lead to a more rapid demise of an older tank.

Nutrient Levels

A saltwater aquarium is not just a tiny piece of the ocean, despite some authors trying to convince us that it is. If we are lucky it will contain some of the same attributes as the ocean but it will always be just a very tiny closed replica of the real thing. One of the major attributes that it will be lacking is size. With this it will also lack the dilution factor that is critical for keeping harmful compounds from accumulating to toxic levels. In the ocean a small amount of nitrate, phosphate or even a heavy metal will not be deleterious to the entire system. In a closed saltwater system however, high levels of any nutrient good or bad will have a negative impact on the system. In a closed saltwater system, one of the factors that lead to old tank syndrome is that over time nutrients will tend to accumulate.

The two major nutrients that will accumulate over time are nitrogen and phosphorous. With large frequent water changes or with the use of resins or specially designed filters it is possible to keep the levels of these compounds low. However as a tank ages and as fish and corals grow these compounds containing these nutrients tend to increase faster and faster. Unless this increase in production of these nutrients is noted and steps are taken to control this increase, these nutrients will become problematic. The first sign that nitrogen or phosphorus containing compounds are becoming a problem is when algae begins to grow in the tank. Algae can grow amazingly fast and while a few tufts of algae on the rock or substrate are not a reason for concern, they should raise a red flag that the nutrient levels are on the rise. However, it should also be realized that nitrate and phosphate levels can be high and algae still might not be present if a large number of herbivores are present. These nutrients have other deleterious effects besides causing algae overgrowth including inhibiting calcification among corals and causing tissue recession from a coral skeleton to name just two of the problems associated with high levels of them.


Detritus can accumulate in the substrate over time if inadequate micro fauna are not present and lead to problems in the tank.

As noted above doing things less frequently is often one of the things that lead to a tank’s not thriving. In this instance the thing that is not done is regular water testing. Regular water testing is essential to maintaining high water quality. When nitrate or phosphate levels begin to rise several things can be done. First more frequent and larger changes with pure aged water should be done. Larger than normal water changes in the 25-50% range are necessary as otherwise the dilution and removal of these nutrients is so small that little is removed and the problem lingers or becomes worse.

If large water changes do not result in the desired diminution of these nutrients then other steps need to be taken. Iron-based phosphate removing resins have increased in popularity within the hobby over the last few years for good reason. These compounds are very good at pulling phosphate as well as heavy metals from the water in a relatively short time. They have proven to be relatively harmless to the tank’s inhabitants including delicate fish and corals. The only shortcomings they seem to possess are the potential to bind with carbonate upon their introduction and consequently pull down the carbonate hardness of a tank for a short period of time and their high cost. Therefore they should be gradually introduced and the carbonate hardness should be tested frequently during their introduction. Nitrate levels can be reduced through several means including the use of refugia containing macroalgae as well as nitrate filters containing anaerobic or anorexic bacteria. For large tanks, a large refugia may be required that may be prohibitive because of its size. Low oxygen filters on the other hand can be relatively small and still remove a great deal of nitrate, but they require significantly more attention and can cause major problems if not maintained properly.

In addition to these nutrients, dissolved organics can also be problematic in an older tank. Signs that this is occurring is that red or black slime, cyanobacteria, begin to form on some of the live rock or on the substrate. Once again as a tank ages and the corals and fish grow the bio-load of the tank increases, that will cause a larger production of these compounds to occur. In addition, filtration equipment such as protein skimmers will tend to function at a lower level over time. In most tanks, water motion will also slow or be reduced over time due to equipment aging and corals growing and this will allow detritus to accumulate. As a result, these factors will work together to cause the organic load within the tank to increase. Even if slime algae does not occur, higher organic levels can be seen simply by the water having a yellow tint to it. Keeping dissolved organic levels low usually requires several things in addition to the increased larger water changes discussed above. Detritus should be removed at every opportunity during these water changes and at no time should large piles of detritus be allowed to accumulate in any one spot. This may require the addition of more water flow within the tank and this flow should be focused along the bottom of the tank to keep detritus in the water column as long as possible so that the filters can remove it. Also when the water is becoming yellow or when slime algae occurs, carbon should be added to the filtration regimen as it is very efficient at removing both yellowing compounds and dissolved organics, but it does become exhausted quickly when these compounds are present in large amounts. Lastly, the protein skimmer should be broken down and cleaned to make sure that it is producing at an optimal level.


Trace Elements

Just as a home aquarium does not contain enough volume to adequately dilute away harmful nutrients, it also does not contain enough volume to supply essential trace elements. As a result over time, some critical trace elements are depleted to such a level that they are no longer present for corals and other animals to consume. At this point, they become the limiting factor for the growth and health of some animals. Unfortunately it is difficult to measure the levels of most trace elements. Fortunately though, many of these trace elements are replenished through regular water changes, so no additions are necessary. However, in some older tanks it may still be a good idea to add a small amount of a wide variety of trace elements on a regular basis. Always start with less than the recommended amount to make sure that the additive is doing no harm. Then gradually build up to the desired amount, which should not exceed the manufacturer’s recommended dosage.


Herbivores like the sea urchin can help keep algae in check, but may mask that nutrient levels are high.


Foods and Feeding

In addition to inadequate trace elements causing problems in a tank over time, improper or inadequate feeding of both the fish and corals can also cause a tank to look old before its time. Just as you would not want to eat steak or lobster alone for every meal despite how good they taste, the same is true or our tank’s inhabitants. We not only need to supply foods in adequate quantity and quality, but we also need to supply adequate variety. On the reef, where we get most of the fish for our tanks, most fish consume 60-70% of their diet in plant material. Unfortunately most of the foods we feed our fish are 80% protein. While this may be fine for lionfish and moray eels, for most other fish this leads to malnutrition or a vitamin deficiency over time. As a result fish that we keep long term in our tanks start to look long in the tooth or worse in a relatively short time. Most of the fish we now keep have been kept successfully in closed systems for over 20 years. If we want to keep our fish looking vibrant and healthy for this long we need to improve our feeding techniques for them as well as provide foods that provide adequate nutrition.


Detritus settles everywhere including the sump, which needs to be cleaned out regularly.

Anyone that has seen a fish that has been kept in a tank with less than optimal food will notice right away that it no longer looks as vibrant as when it was added to the tank. For this reason it is apparent that we need to supply our fish with significantly more foods that contain the compounds that not only keep them healthy, but also keep them vibrantly colored. There are now foods available, fresh, frozen, and freeze dried that contain not only high levels of plant material, but also that contain essential pigments to keep the fish looking vibrant. If none are readily available you can even prepare your own food mix using foodstuffs available at the fish market and grocer using recipes found easily on the Internet. It is not only crucial to feed these foods, but it is just as important to feed them properly. Feeding should be done frequently in very small amounts. The stomach and digestive tract of most fish are very small. They are designed for the constant consumption of small amounts of food rather than to take in a large bolus of food in one big meal. Unfortunately, feeding one large meal to our fish per day is how it is usually done. This methodology too needs to change in order to prolong the health and vibrancy of our fish long term.

In terms of feeding coral and other invertebrates, only now are we starting to understand the need to feed these animals. Most of us assumed that adequate light and the extra food and waste from our fish would be more than adequate to supply the nutritional needs of our corals. However, when analyzing the structure of a coral polyp it becomes apparent how crucial food intake is when one realizes that 60% of a coral polyp’s body is designed for food intake. It is highly unlikely that this much of the coral’s body would be dedicated to such an endeavor if it were not critical for the long-term health of the animal. In terms of animals looking less than optimal as is the case in old tank syndrome, inadequate nutrition for the invertebrates may at least partially explain this along with the other factors previously discussed. When the corals are small it may be possible for them to obtain all of the nutrition they need from the light and from the extra food and fish waste floating around. However as the colonies get larger and competition between corals for food and space more intense it is likely that the nutritional needs of the invertebrates are no longer being met and hence they no longer look to be in optimal health.


Excessive algae growth is indicative of excessive nutrients being present.

I have been conducting a relatively simple experiment for the past year in my own relatively older systems (both over 5 years of age). In one tank the invertebrates are on their own and only get nutrition from what is left over from the fish or what they take from the water. In the other system the corals are fed directly three times a week with different foods. For the first six months there was virtually no difference in the overall health of the corals or the tank in general. However over the last six months I have noticed a significant difference. The corals in the tank being fed havegrown significantly more than those in the tank that was not fed. (I know this is probably not a big surprise). But the big surprise is that the corals in this tank also suffered virtually no losses while several colonies in the non-fed tank perished or suffered tissue loss at some point. After observing this first hand it is now my opinion that feeding the corals and other invertebrates on a regular basis will go a long way in keeping them from pushing the tank into looking haggard.



One of the other causes of tanks looking old is that over time many pests become problematic. Flatworms, aiptasia, red bugs, Majano anemones parasitic brittle stars and other pests tend to reproduce and thrive in closed systems where predators are not present. When a tank is first set up and often over the first few years these pests are usually not in adequate numbers to be a problem. Over time and with a ready food source these animals can constantly irritate or even kill many sessile invertebrates. For this reason it is essential that pests be removed or killed as soon as they are spotted in a new or relatively new tank, lest they reproduce to harmful levels. There are now numerous accounts of how thriving tanks needed to be completely broken down as a result of these pests overrunning the tank. While these are extreme cases, even small numbers of these pests can make the animals in an old tank look damaged or sickly.


Speciation / Competition

The opposite of having the corals in an old tank look less than optimum due to parasites is to have them look this way due to speciation. Speciation is the process whereby one animal or plant species dominates a locale after multiple species were present. The best example of this is an old growth pine forest. In this type of forest only pine trees thrive. This is due to the pine trees themselves producing compounds in their needles that prevent other plants from growing. As a result as the pine tree drops its needles the compounds in the needles act as an herbicide and prevent other plants from growing under or with the pine trees.

In a saltwater tank, especially one housing soft corals such as Sarcophytons, Xenia, Sinularia or Cladiella one of these species will tend to dominate over time. All of these corals produce terpenoids or sarcophytenes. These chemicals just like those found in pine needles act to inhibit the growth of competing animals. As a result, as a tank ages the animals that produce the most growth inhibiting of these compounds will tend to dominate. This same type of phenomenon also happens on the reef where huge stands of a single species of soft coral occupy specific areas of the reef. While having only one type of coral in a tank actually is probably more representative of a section of the reef, most hobbyists do not like this look and desire diversity. However, the corals present will still produce terpenoids to try and produce this result. This production of growth inhibiting compounds does take its toll over time and the result once again is corals and other invertebrates that look less than optimal.

There are several things that can be done to prevent this from occurring. First, water changes, once again, and the use of carbon can help to dilute the concentration of these growth inhibiting compounds. In addition, it may be necessary to thin out or reduce the size of large soft coral colonies. This is necessary in that larger colonies can produce larger amounts of these compounds. So in order to prevent one species from dominating a tank, it may be necessary to “prune” the corals to keep them all to relatively equal size or of an equal ability to produce toxic compounds.

Competition between corals is another factor that may cause corals to look sickly. If two or more coral colonies have to constantly battle each other for space, nutrition, etc., these battles consume a lot of the animal’s energy. As a result the corals lose a lot of their vitality. For this reason it is essential to give the corals lots of space when initially setting up a tank to try and reduce this competition. When this is done an interesting phenomenon occurs, especially with stony corals. The corals will eventually grow to the point where their bases almost touch each other. But at this point they kind of form a demilitarized zone where neither coral grows into the other. This behavior allows both corals to thrive without requiring either coral to devote a lot of energy to defending itself or attacking its neighbor unlike what occurs when two corals are placed too close together.


Diminished Diversity in live rock and sand beds

One of the great attributes of new live rock is the vast diversity of life that it contains. Mysis, shrimp, copepods, worms, crabs and numerous sessile invertebrates abound on this substrate. A new substrate is also often colonized from the animals in the rock so it to can hold a large number of different organisms. Over time however, the diversity in the rock tends to be reduced. Microfauna are consumed, reproduction in some species does not occur in closed systems, the substrate becomes clogged with detritus and the overall variety of life diminishes. This diversity does not simply exist in the rock and substrate, it helps remove waste, it is consumed by the fish and corals it keeps the substrate oxygenated, etc. As a result, it is possible that as the diversity of this life is reduced, the overall health of the tank may be reduced as well. To try and keep this from happening new live rock that has been properly and completely cured should be introduced from time to time. This will help to add diversity back into the system and hopefully help to keep the tank more vibrant. Detritus should be removed regularly from the substrate to not only keep it from becoming a nutrient sink, but also to allow the animals living within it space to occupy. It may even be a good idea to regularly remove some of this old substrate and replace it with new. It is also now possible to add commercially raised microfauna to the substrate to add to the diversity. All of this may help to keep the diversity within the tank as high as possible.

Not all older tanks have to necessarily go through old tank syndrome. If the tank is properly maintained as outlined above and few shortcuts are taken it is possible to have a tank look as vibrant at ten years as it did at two. To most serious hobbyists a tank does not even start reaching its peak until it is at least two years of age. It is unfortunate and unnecessary if we let our tanks pass through this level of optimum appeal in a very short time.

1 Comment

  1. S.R.

    This is mostly a very good article, but “speciation” is the formation of new species by the process of evolution, not the domination of one species over others in the environment. I don’t know that anyone has ever observed speciation in a reef tank, cool as that would be.


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