Aquarium Fish Tank

An aquarium is a pool or tank of fresh or salt water in which fish, other aquatic animals, and water plants are kept for exhibition and study. Many hobbyists keep small aquariums at home, and many public aquariums throughout the world are maintained for the enjoyment and education of visitors. Others, although open to the public, are devoted primarily to the scientific study of water plants and animals.

The two major kinds of aquariums are the controlled aquarium and the balanced aquarium. The controlled aquarium requires aerators, filters, and other mechanical aids to maintain the fish and plant life. A balanced aquarium is one in which the oxygen and carbon dioxide needed to support aquarium life are provided in proper amounts by the tank's inhabitants. The oxygen needed by the fish is supplied as a waste product from the plants in the tank, and the carbon dioxide that is needed by the plants to make food is supplied as a waste product of the fish's respiration. In a simple home aquarium, a small number of fish can be kept without the aid of aerators or plants.

The bottom of the tank should be covered with a 1 to 3 inches (2 to 7 cm) layer of clean, coarse gravel. The gravel is used only as a base in which to root plants. It should not be deep, or food will settle in it, decay, and pollute the water. Fine sand is not recommended because it prevents water circulation. Coral, seashells, and some kinds of gravel that contain lime must be avoided because they react with the water and produce substances harmful to fish.

Plants are both decorative and useful in aquariums. Some fish eat plants, and others lay eggs in them or place their young among the leaves for safety. In balanced aquariums, plants are a necessity since they are the only source of the oxygen needed by the fish. Some popular aquarium plants are fish grass, elephant ear, duckweed, eel grass, and several kinds of Sagittaria. A few snails, which eat accumulations of algae, may be added to keep the tank clean.

Although aquarium plants need light to thrive, direct sunlight is often harmful to fish. For this reason, the tank should be placed in a well-lighted but not too sunny part of the room. If the room is relatively dark, the tank may need to be lit artificially.

Although nearly all running water is suitable for aquariums, heavily chlorinated water may kill fish. Chlorinated water that is to be used in fish tanks should be exposed to the air for 24 hours to allow the chlorine to diffuse out of the water.

The temperature of the water should be regulated to suit the kind of fish being raised. For most tropical fish, a temperature of 70° to 85° F. (22°-29° C.) is warm enough. A glass cover placed over the top of the tank helps maintain an even temperature. It also prevents the fish from leaping out of the tank and keeps dirt and soot out. With the exception of a balanced aquarium, a completely covered tank must be supplied artificially with fresh air.

Among the most useful accessories are filters, aerators, and heaters.

An aquarium filter contains sand, activated charcoal, glass wool, or other filtering materials. Water from the aquarium is pumped through the filtering material and then returned to the tank through a tube. As the water passes through the filter, waste gases and particles of dirt are removed by the filtering material.

An aerator is a small electric pump that forces air through a tube opening at the bottom of the tank. The air comes out as a stream of small bubbles which release oxygen to the water. A tank with an aerator can sustain twice as many fish as an unaerated tank.

An aquarium heater consists of a small tube containing an electric heating coil. Some heaters have a thermostat that automatically maintains an even temperature by turning the heater on and off.

Most fish thrive on a varied diet of prepared fish food, chopped worms, and small pieces of fish, meat, or shrimp. Fish should be fed twice a day and given no more food than they will eat in half a minute to two minutes. The particles of food should be sprinkled on the water's surface. Any food that is not eaten should be removed, so that it will not sink to the bottom and decay.