When an aquarium is initially setup, there is insufficient beneficial bacteria to break down fish waste and uneaten food, which allows for unhealthy levels of ammonia and nitrite to build up. Hobbyists refer to this situation as “New Tank Syndrome”; it is a leading cause of fish deaths with newcomers to the hobby. Over time the addition of fish waste, carbon dioxide, light, and plant fertilizers will begin to build large colonies of beneficial bacteria that will ensure the aquarium remains healthy and active.

The primary source of ammonia (NH3) is created when fish consume food and oxygen (O2) and create waste and carbon dioxide (CO2). The fish waste then decays into Ammonia. Other sources include excess food that is not eaten as well as decaying plants and dead fish. The rise in ammonia triggers the growth of Nitrosomonas which produce nitrites (NO2). The nitrites trigger the growth of Nitrobacter to produce nitrates (NO3). The nitrates and carbon dioxide are consumed by plant life which produce oxygen through the process of photosynthesis. Excess nitrates are removed by water changes.