What is the Nitrogen Cycle?
Fish waste, uneaten food, and decaying plant matter all produce ammonia. Ammonia is poison to your fish and must be removed. When ammonia is present in an aquarium, a bacterium called Nitrosomonas will start to form. Nitrosomonas oxidizes ammonia and puts off a byproduct called nitrites. Nitrites are also poisonous to fish but less than that of ammonia. In the presence of nitrites, a bacterium called Nitrobacter will form which converts nitrites into nitrates. Nitrates are significantly less poisonous to fish and are removed from a tank by doing water changes. Plants will also feed off of nitrates so having a planted tank can slow the build-up of nitrates in an aquarium