cycle

An aquarium’s nitrogen cycle is a process by which nitrogen-containing compounds are converted into other compounds. The cycle is important in the aquarium because it helps to keep the water clean and the fish healthy. The cycle is started by the addition of ammonia to the water. Ammonia is converted into nitrites by bacteria. Nitrites are then converted into nitrates by other bacteria. Nitrates are used by plants to grow. The cycle is completed when the plants are removed and the nitrates are converted back into ammonia.