Ammonia can be removed by using a liquid ammonia remover that is placed directly in the water, or ammonia chips, which are put into the filter. The primary means of removing ammonia and nitrites should always be your biological filter. If you need to medicate your aquarium, you'll need to remove the carbon when treating the sick fish. Otherwise, the carbon will absorb the medication. A well-established aquarium is a natural ecosystem in which your fish and the beneficial bacteria that naturally occur in an aquarium depend upon each other to live happily and healthy.
Fish eat and produce ammonia as a waste product.
Excess food and plant materials also decay and produce ammonia. Beneficial bacteria neutralize the ammonia and produce nitrites, which in turn are neutralized by other beneficial bacteria that produce nitrates. Nitrates in normal levels are harmless to freshwater fish. The only thing that you need to do is ensure that you start with a good biological filtration system and that you maintain it. The water must be oxygenated.