It is a common belief among many people, including many aquarists, that "chemicals" are "bad", and "natural" is "good". I have heard otherwise fairly knowledgeable aquarists warn me against using "chemicals" in my tanks, because they will upset the "natural balance" of the tank. While the goal of the aquarist is or should be to replicate a natural system as closely as possible, an aquarium simply is not natural, and therefor cannot precisely duplicate nature. The natural state of an aquarium is to progress toward ruin, and without some intervention from the aquarist the fish would waste away. So just what is this intervention? The judicious addition, removal, and responsible use of chemicals.

Just what are chemicals, anyway? Chemicals are the substances from which all matter is formed. While most people know this, they often seem to forget it. It is impossible not to use chemicals in the maintainance of an aquarium. The water, the fish, the food, the gravel, plants and filter material are all chemicals that affect the chemistry of the aquarium as a whole in many ways. It is therefor impossible to successfully maintain an aquarium for any length of time without at least some knowledge of chemistry, especially as it applies to pH, water hardness, buffering capacity and the "nitrogen cycle".

Does this mean that chemicals are actually good? Well, no. Chemicals are not good or bad. They are just unavoidable. A chemical is good for a given purpose if it performs a desired function, and bad for that purpose if it intervenes. This means that if your purpose is keeping a breeding pair of discus alive, an excess of calcium salts is definitely bad. But if you are keeping a reef tank full of hard corals, then those calcium salts are a necessity! This is where you, as an aquarist, need to use judgement and knowledge to use the correct chemical for the correct situation. But, of course, it is not as easy as adding the right chemicals to the tank and then just sitting back and leaving them. The chemicals change as they go through reactions. This happens due to several factors. First, you must add food to your aquarium. This food contains chemicals - some of which immediately leach into the water. Phosphorus is a good example of this, as are many Calcium and Sodium salts. These directly affect the tank's chemistry. Further, the food is then eaten by the fish or, under less-than-ideal situations, it sinks to the tank bottom and rots. When the food is eaten, the fish digest the food for nutrients and energy. What is left is the end result, or by-product of digestion. This includes many chemicals, including Methane, Carbonic Acid, organic waste, and most importantly Ammonia. These are all fairly easily classified as "bad" chemicals in that they all work against our purpose of keeping healthy fish. That is why fish excrete them! If the food is not eaten, it rots, the same as the organic waste or "mulm" the fish excrete, and produces many of the same chemicals. These "bad" chemicals can build up and become lethal to aquarium life if not removed or changed into less harmful chemicals. Fortunately, the aquarist is not exactly alone in this effort. Nitrifying bacteria are his allies in transforming the deadly Ammonia into Nitrite and further into Nitrate, a chemical which is much less toxic to fish than Ammonia.

There are many articles detailing this process, so I will not elaborate too much on it here. This process is refered to as the Nitrogen cycle, and is the basis of most forms of biological filtration. The idea is to provide these beneficial bacteria with the optimum conditions for them to carry out this reaction. They must have access to nutrients, which are Ammonia and the Nitrites, and they must have access to another chemical, Oxygen (O₂). Oxygen is definitely a "good" chemical in the aquarium. Under normal conditions it is almost impossible to have too much oxygen in the aquarium water. Oxygen is most soluble in cold, chemically pure water and is least soluble in warm water in which many other chemicals are dissolved. Therefor fresh water can contain more oxygen than saltwater, and temperate tanks can hold more than warm, tropical ones. Other factors affecting the amount of oxygen in the water is the pH and the tank's general "cleanness". Extremes in pH or high concentrations of Ammonia can drive the oxygen content in the aquarium dangerously low. That is why it is important to measure these qualities periodically.

To maintain the proper amount of oxygen, good circulation is essential. Oxygen is dissolved at the water surface, and therefor fresh water must be constantly stirred to the top to dissolve more of this precious chemical. Only in certain planted tanks should this not be the case. This is because the Oxygen is then provided by the plants, and too much surface motion will drive out the Carbon Dioxide (CO₂) that the plants require to produce Oxygen.

In time, however, many of the chemicals, both benign and malignant, will build up even with adequate oxygenated bacteria. The pH will tend to drop and the general hardness will increase as evaporated water is replaced with fresh water containing more chemicals. Eventually the water will inevitably become unsuitable. This is why it is necessary to do water changes. There are many rules of thumb about how much and how often, but 20-30% every week is usually adequate in most cases. This process physically removes part of these unwanted chemicals from the tank each time. There is no filter on the market that can do this for you.

There are other times when it might be necessary to add additional chemicals to the aquarium. A good example of this is when mixing salt water for a marine tank. Sea water contains a large number of chemicals, including salts and trace elements, that are necessary for oceanic life forms. These chemicals affect the density, pH, conductivity, and many other physical characteristics of the water.

Another example would be the addition of peat or peat extracts to soften and acidify the water, or when adding buffers to increase the water's buffering capacity. Adjustments in pH must be done gradually and cautiously, as this greatly affects the aquarium's inhabitants. A fish's body chemistry is directly affected by by that of its environment; much more so than ours is. A stable chemistry that is less than ideal is far superior to one that drifts constantly, even if it is closer to your "goal" chemically.

Sometimes chemicals may be added for entirely different reasons, such as treating sick fish or eradicating snails or algae. These can be very risky, as they sometimes have far-reaching effects. It is always best to medicate sick fish in a "hospital tank," and it is also a good idea to find more "natural" remedies where possible. Most often, people try to treat the symptoms without finding the underlying cause-be it inadequate heat, wrong pH or hardness, or an excess of pollutants in the water. In the case of algae, an abundance of Nitrates or Phosphates may be the problem. A good water change is the best way solve this, although there are many products on the market that can be added to your filter to chemically remove them. If the problem persists, you should look for an underlying cause, such as overfeeding or feeding the wrong foods. Some commercial fish foods contain high levels of added Phosphates. These can build up in the water and could possibly affect your fish's growth, and definitely encourage unwanted hair algae.

Snail remedies should never be used in an aquarium. Even if the remedy itself is harmless to fish (which is very questionable), the dead snails definitely are not. Hand picking them out of the aquarium is time consuming, but safe. Many fishes, such as clown loaches, eat snails. If all else fails, drain the tank and remove the gravel. Soak it in a bucket of hot (boiling) water for a few minutes and rinse it well. Try to rinse as many dead snails from the gravel as possible. Remember that any nitrifying bacteria that the gravel had before will now be dead, so in essence you are starting over in the Nitrogen cycle. A final possibility is to abide the snails. They are usually harmless and provide the services of consuming algae and waste food and aerating the substrate. Too many snails can, however, affect the chemistry of the tank by using Calcium to build shells and by adding to the bioload of the tank. Chemical remedies alter the water in ways the fish are not used to, and may stress them. Also, the medication may kill off all of the nitrifying bacteria, especially when using antibiotics, thus disrupting the Nitrogen cycle. In addition, mixed medications may react with each other and have dangerous results. If you are not sure what you are doing, consult someone who is before using medications.

The substrate and decorations can also affect the chemistry of the water. Crushed coral and calcereous substrate and rocks like dolomite or limestone leach chemicals into the water that will raise the pH and hardness. This may be a good effect or a bad one, depending on the type of fish that are being kept in the tank.

To test a rock for this trait, try dripping Acetic Acid (vinegar) on it. If it begins foaming, then it is calcereous and will affect the chemistry of the tank. Driftwood also affects the water chemistry. If it is not the correct type of driftwood, it may rot, adversely affecting the water chemistry. If it is of the type generally accepted as "safe" to use, then it has been treated with Tannins, either naturally or commercially, and will not rot in the aquarium. It will, however, slowly release these tannins into the water, gently acidifying and darkening it. Some people find this coloration pleasant; others do not. It is certainly not unnatural for many fish which come from such waters-discus and many other forest dwelling fishes come from waters so steeped in Tannic Acids that from a distance they appear black.

Plants affect the water chemistry by using Carbonic Acid (Carbon Dioxide or CO₂) and Nitrogen to grow. They also require Oxygen, the same as animals do. During the day, however, while photosynthesizing they produce more Oxygen than they use, and respire the surplus into the tank. In an aquarium with many plants, the pH will go up as the lights are turned on and the Oxygen content will rise. That is because the plants are using more CO₂ and producing O₂. But at night, the CO₂ rises and the O₂ drops. Plants can adversely affect the water chemistry if dead leaves are left to decay. Plants should always be kept clean and free of decaying tissue.

In nature, the biosystem is so large and complex that the balance is maintained steadily, and small changes are easily absorbed by the system. Large changes, however, have a definite effect on the local biology. In an aquarium, errors are much less easily absorbed by the limited system. That is why it is important to regularly monitor and keep records of the aquarium's condition. With just a little bit of knowledge about your tank's chemistry, you should be well on your way to mastering the art and the science that makes up this hobby!
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