Ammonia is the most lethal form of inorganic nitrogen produced in aquarium water.

The major source of ammonia in a well run aquarium, is from solid waste of fish and invertebrates, uneaten food, decaiyng leaves of plants.

Nature comes to our rescue as there are specialized bacteria (Nitrosomonas species) that "eat" ammonia , and strip away the hydrogen atoms. By the way, this bacterial population may be affected by many negative biochemical events.

In an established aquarium Ammonia should be zero, for these reason, the periodical analytical valuation of ammonia in the aquarium water should be considered by the serious aquarium enthusiast.