In a balanced aquarium, plants and animals live together easily by helping each other. The animals give off the gas carbon dioxide. The plants use this gas and in turn give off oxygen, which the animals breathe. This produces an aquarium that needs little attention. It is necessarv only to feed the animals, clean the tank now and then, add fresh water, and supply enough light.
Scientists differ on the value of the balanced aquarium.
The first apparently successful balanced aquarium was made by Dr. Philip H. Grosse in 1852. The best type of tank has a metal frame, glass sides and ends, and a slate or glass bottom. It should be placed in strong light, but not in direct sunlight. The bottom should be covered with one or two inches of clean sand mixed with gravel. Many types of water plants may be used, but those which furnish the most oxygen are vallisneria, sagittaria, and anacharis.