What is a Balanced Aquarium?

Originally the concept of a balanced aquarium was that the standing aquarium is a self-contained microcosm - a little world. The theory ran that as the plants manufactured food through the process of photosynthesis; they utilized carbon dioxide and gave off oxygen. Fishes, on the other hand, gave off carbon dioxide and utilized oxygen. Fishes’ waste, according to the theory, fertilized the plants, while excess plant growth provided food for the fishes. One thing thus balanced another, and no outside care was required.

Unfortunately this theory simply does not hold up in practice. While plants do give off oxygen in excess of what they use for respiration, they do so only in the presence of bright light. When the aquarium is dark, they use up oxygen just as do the fishes. Water cannot store more oxygen than the amount required to keep it in equilibrium with the air above it. Excess oxygen passes off readily. The same does not hold true of carbon dioxide. It tends to stratify, forming layers along the bottom. (Circulation prevents this stratification.) Having a maximum air surface in proportion to the depth thus goes a long way toward keeping the aquarium properly “balanced.”

The waste matter produced by the fish is far in excess of the amount required by the plants. Moreover, most of our aquarium fishes are carnivorous, eating animal, not vegetable, matter. Even the more herbivorous species require some animal food.

So the idea of a “balanced aquarium” is a fallacy in its original concept. An “aquarium in balance” is, however, what can be achieved.

The factors that modify an aquarium more or less balance each other includes the proper amount of light (too much over stimulates algae, too little does not permit plant growth); the proper amount of food (too little stunts the fishes, too much pollutes the aquarium); the proper number of fishes; the correct size of aquarium, and the proper temperature, etc. All of these things must be in proper “balance” with respect to themselves and the others if the aquarium is to flourish.

Aquarium Plants

Under the influence of sunlight, plants and only plants have the ability to manufacture their own food. These green plants combine water and carbon dioxide to form sugars in a process known as “photosynthesis.”

During this process, free oxygen is released in excess of that used by the plant for respiration. This occurs only under the influence of bright light. At other times, the plant breathes normally, consuming oxygen and giving off carbon dioxide. Photosynthesis occurs only when the plant in light is healthy and growing.

Light, then, is essential to your aquarium so that the plants will grow properly and give off oxygen and consume carbon dioxide. The “wonder material” that regulates the food manufacturing process is chlorophyll - the material that gives plants their green color.

There is a good deal of controversy concerning the amount of oxygen that the aquarium plants actually supply for fishes to use.

It should be remembered that water can dissolve only a certain amount of oxygen; any excess oxygen is therefore released at the surface. It is not stored in the water for later use as the fishes require it. Carbon dioxide is released and oxygen is taken into the water. The process can be hastened by bubbling stream of air through the water. This tends to agitate the water and increase the area exposed to the surface in proportion to the amount of circulation engendered. Manual stirring of the water serves the same purpose, but it is not so convenient a method as the mechanical one.

The greater the area of the exposed-to-air water surface, the faster oxygen will be taken in and carbon dioxide released. The greater the air surface, the more fishes can be kept in a given volume of water. You do not really increase the capacity of the fish tank to hold fishes simply by raising the height of the water in the tank. You must also increase the other dimensions in proportion.

Probably the same number of fishes could be maintained in a bare aquarium as in one with plants. Then, you may ask, why bother with aquarium plants? Well, plants serve many functions besides the disputed one of oxygenating. The principal function is an esthetic one: there would not be much beauty to a tank without plants. They provide an excellent background against which your colorful fishes will display themselves to best advantage.