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Old Tank Syndrome

It happens to the best of us. It was great when it started, but after a while the excitement of newness begins to wear off. You no longer rush home just to be near, and your desire to meet every need has diminished to the point where you just seem to be going through the motions. The honeymoon's over; you take for granted the things you once cherished. You hope it's just a phase, but deep inside you fear you're headed for....

Old Tank Syndrome.

OK, so maybe it's not quite true that "Aquariums are People, Too". But the analogy may be worth considering: a neglected or poorly maintained aquarium may superficially appear to be doing just fine, but disaster may be brewing beneath its surface.

Perhaps the most important concept to bear in mind is that home aquariums are very "closed systems" - in essence meaning that, with few exceptions, everything we put in the aquarium stays there, in one form or another, until we take it out. That ten ounce can of flake food, two bottles of water conditioner, and even the chemicals present in the top-off water added during the last six months, are all still in there somewhere - unless we have taken steps to remove them. Some of these chemicals will now be in "good" forms (for example, much of the protein in the fish food will hopefully be in the form of bigger, healthier fish), but others will occur in forms more detrimental to the well-being of our prized pets.

The first, and perhaps best indicator of potential problems is rising nitrate levels. As the end product of the breakdown of fish waste, nitrate is released into the water on a continual basis. In a neglected aquarium, nitrate accumulation knows no bounds, sometimes reaching several hundred parts per million. Many invertebrates and some fish are directly affected or even killed by high nitrite levels, but elevated readings should be of concern even to keepers of hardier fish. If nitrate levels are continually rising, it can be assumed that other, more threatening but harder to test, compounds are accumulating as well.

The same processes that reduce ammonia to nitrite to nitrate also produce an abundance of hydrogen ions, which, if left to their own accord, acidify the water. In water from some sources that contain few "buffers" (ions that help stabilize pH by combining with excess hydrogen or hydroxyl ions), pH will tend to decline steadily just as the nitrate increases, and again regular pH testing may help alert the aquarist to impending trouble. However, in more heavily buffered water, an interesting but more threatening phenomenon occurs. As hydrogen ions are produced, they are immediately tied up by the buffer ion, and the pH remains roughly the same - until all the buffer ions are used up. At this point, the pH drops rapidly, and this sudden "pH crash" can be very damaging to fish.

If this process is allowed to continue (and a few, very hardy fish survive), another interesting biochemical phenomena occurs. At a pH of about 5.5 or less, the bacteria that usually convert ammonia to nitrite are inhibited, so ammonia levels begin to rise. Strangely, though, the low pH actually protects the remaining fish by keeping the ammonia in the non-toxic ammonia (molecular) form instead of the very toxic ammonium (ionic) form! It is not uncommon to see an old, neglected tank with a pH reading off the bottom of the chart, ammonia and nitrate off the top, and a couple of old-timer fish still swimming about.

In some cases, aquariums get little maintenance, but need to be "topped off" regularly with additional water to replace that which has evaporated. If the source water is buffered and its addition frequent, the pH crash and resultant ammonia rise might be forestalled, but a new problem is encountered. When water evaporates, only pure, clean, H2O leaves the system; all the other minerals and impurities are left behind in the aquarium. Adding more water means adding more minerals (and by definition buffered water has significant amounts of minerals), in effect concentrating them. Such aquariums often show acceptable pH and ammonia levels, but high nitrates and hardness.

In some rarer situations, notably in "natural" or some reef aquaria in which plants, rather than bacteria, are the primary nitrogen consumers, the inhabitants could be suffering even if nitrate and ammonia readings are very low, and pH steady or a bit high. Rarely is any aquarium so well balanced that no by-products are accumulating and no necessary elements are in decline.

In either of the above scenarios, the fish that survive such declining water quality often become mere shadows of what they could be. Poor conditions limit growth and color, and may contribute to conditions like "hole-in-the-head" and " head-and-lateral-line-erosion". In fact, the old myth that "a fish will only grow to the size of its container" may well be attributed to the stunting that occurs in poorly maintained aquariums. Other fish may appear to remain unaffected, at least to the casual observer, which may lead to yet another calamity.

An unwary aquarist is most likely to be rudely awakened to Old Tank Syndrome when he attempts to add new fish to his existing collection. Many fish "shock out" upon introduction to this very different, harsh environment and simply perish within a few hours. Others may survive the initial shock, but the acute stress of this radical change in environment weakens them, making them more susceptible to infection. Ironically, disease-causing parasites may well be so successful at attacking these weakened fish that they quickly multiply to epidemic proportions, and wreak havoc on the original residents as well.

The aquarist might be inclined to blame the dealer for "selling sick fish"; after all, he hadn't lost any fish or seen a sign of disease in several months - or maybe years - before making this purchase. "Obviously," he argues, "there's nothing wrong with my aquarium, or all my fish would have died long ago". But that isn't necessarily the case. The original inhabitants had the opportunity to become slowly accustomed to waste buildup. The hardier specimens adapted to the chronic stress and survived. Weaker individuals were overcome one at a time, perhaps over a period of months, and their deaths attributed to natural causes.

We'll leave this aquarist and dealer to wrangle over replacement policies, just as many others have done before them, but hopefully take with us the knowledge that such tragedies don't need to happen. Good, regular aquarium maintenance is both the prevention and cure for Old Tank Syndrome.

Filtration - at least "mechanical" and "chemical" filtration - can remove some specific compounds from the water, providing the filter media is cleaned or discarded periodically. "Dirt" that is stuck in a filter cartridge or adsorbed in a chemical media is still part of the aquarium environment until the cartridge or media is removed from the filter. Interestingly, "biological" filtration does not actually result in the net removal of waste; it simply converts one form into a different, hopefully less dangerous form (for example toxic ammonia is converted to less toxic nitrite and then into relatively safe nitrate).

But no filtration system removes everything, and there tends to be a continuous accumulation of waste products and other compounds in every aquarium until - you guessed it - a water change is performed. A 25% water change removes 25% of the nitrate and ammonia and restores 25% of the buffers, all in one fell swoop. Water changes can be performed as often as desired, assuming that there is suitable water readily available, and should be performed as often as necessary to keep nitrate and pH levels stable. A typical aquarium might require a minimum of 25% changed every two to four weeks, while a crowded or overfed tank may need to be serviced weekly.

If a tank is found to be experiencing Old Tank Syndrome, water changes are again the treatment of choice, but care must be taken not to attempt too great a change at once. Sudden changes in environment are always stressful to fish, even if the changes are for the better. Furthermore, if the aquarium has already gone into the low pH / high ammonia phase, a rise in pH will change non- toxic ammonia into lethal ammonium and lead to catastrophe. Daily changes of 15% to 20% are safer and as effective as the one-time 50% to 90% cleaning we might be tempted to perform. Constant monitoring of pH, ammonia and nitrate are highly recommended during this process. If ammonia levels remain high while pH is being raised, it is wise to back off the water changes for a few days to allow the ammonia-eating bacteria the chance to catch up.

Once proper conditions have been restored, a regular maintenance program, including water changing, filter cleaning and perhaps chemical testing, should be set up and followed. A well- maintained aquarium is a thing of beauty and wonder, and who knows, it just might rekindle a long-lost flame.


This article originally appeared in
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Aquarium Fish Magazine

Copyright © 1999 James M. Kostich
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