Aquarium keeping in the Western World is a fairly recent hobby. The keeping of fish in small indoor tanks was seriously undertaken only in the middle of the last century, when both in Britain and on the Continent of Europe a considerable interest in the subject developed. It is not surprising that the hobby as practiced then was short lived, as the principles governing successful aquarium maintenance were little understood and their practice confined to few.
At the beginning of the present century aquarists both in the United States and in the Old World began to keep tropical fishes, and it was perhaps the essential artificiality of so doing that started a new wave of more successful fish culture. The older aquarists were obsessed with copying nature in their tanks - or rather with the attempt to do so - whereas the keepers of warm-water fishes had to experiment with their charges and create suitable environments for them.
Often they started only with the knowledge (or assumption) that the fish must be kept warm, and this in itself raised problems of quite new types, including the death of favorite weeds and water snails at higher temperatures and the more rapid fouling of water with
The Rectangular Tank
The old-fashioned fish bowl is entirely unsuited to its purpose. It has been almost completely replaced for serious fish-keeping by the rectangular glass tank, either made wholly of glass or with a metal frame and glass sides and a bottom of glass, slate, or other rigid material.
Except when used for spawning, for exhibition purposes, or as a hospital tank for the treatment of disease, the tank contains growing, rooted plants; these are set in a sand or gravel layer 1 or 2 inches thick. There may be decorative rocks, but the chief decoration is usually the plants themselves, which contribute more to the attractive appearance of a well set-up tank than do the fishes.
Such a tank is usually between 5 and 25 gallons in capacity; a 15- gallon tank measures 24 X 12 X 12 inches and is a favorite size. Smaller tanks than these cannot house many fish or allow proper development of the plants.
Larger tanks are very attractive and give scope for beautiful planting arrangements and for fine growth of the fishes, but they are expensive and not likely to become generally popular. Most fanciers therefore prefer a range of medium tanks rather than one or two very large ones, but it must be emphasized that fine fishes can be grown in large tanks.
In general, tropical fishes can be housed in smaller tanks than cold- water fishes. This is because they are usually smaller and are also better able to withstand a relative deficiency of oxygen in the water. Size for size, most tropical fishes can be crowded a good deal more than the common goldfish and very much more than fancy varieties of goldfish. A 15-gallon tank might comfortably contain a dozen 3-inch rosy barbs, four or five 3-inch common goldfish at the most, and not more than a pair of Orandas of the same size.
The Balanced Aquarium
Animals (including fishes) consume solid food and excrete solid feces. They breathe oxygen and exhale carbon dioxide, and thus in total they tend to deplete their environment of oxygen and to foul it with carbon dioxide and excrement.
Plants also breathe oxygen, but in sufficiently bright light they manufacture sugars, etc., from carbon dioxide taken from their surroundings, whether air or water, and they release oxygen. This is done in the green leaf. They also absorb dissolved salts and use these together with carbon dioxide in building up complex organic compounds. Very few higher plants can utilize solid or very complex substances, and before animal excrement (usually known as "mulm" in the fish tank) is available to them it must be broken down by fungi or bacteria and made soluble.
Thus plants, in adequate light, tend to restore oxygen to the environment and to remove the waste products of animals. In poor light or in darkness they deplete the water or air of oxygen just as animals do. It is only in the daytime, or under bright artificial light, that they perform the complementary function to animals.
From these facts grew the concept of a balanced aquarium, with the waste products of the fishes absorbed by the plants, and the oxygen necessary for the fishes provided by the action of the plants in light. A well-planted tank with adequate illumination will usually stay clear and sweet for months or years with little attention.
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