Biological Filtration Biological purification of water is accomplished by various beneficial strains of bacteria.

There are several important sources of waste produced in most aquariums. Fish generate nitrogenous waste as they breathe and excrete organic matter. Plants shed leaves as they grow. Invertebrates and corals also shed organic substances. Beneficial bacteria known as Nitrosomonasand Nitrobacter, commonly referred to as nitrifying bacteria, prefer lodging in the filter system. Superior oxygen levels exist due to constant incoming water, while biological filter media provide an excellent habitat for these desirable bacteria. Nitrifying bacteria utilize two very toxic nitrogenous compounds, ammonia and nitrite, as an energy source, and produce nitrate, a relatively harmless by-product. Nitrate is easily controlled through regular water changes and is used by plants as a food source.

The Nitrogen Cycle (see chart) refers to the conversion of toxic nitrogenous compounds, ammonia and nitrite to nitrate. This phenomena is commonly encountered when first starting an aquarium, or if certain events take place which eliminate or reduce beneficial nitrifying bacteria, such as disease treatments or prolonged power failures. Bacteria take time to establish themselves. Nitrifying bacteria reproduce every eight hours.

The initial nitrifying bacteria to populate tend to be Nitrosomonas, which convert ammonia to nitrite. This takes approximately ten days. The levels of ammonia during this stage are often toxic and fish populations should consist of a few very hardy species. Additional water changes are recommended, always ensuring that pH levels are not increased (to avoid increasing the toxic ammonia component, NH3). The use of Cycle is highly recommended to introduce significant quantities of ideal bacterial strains, critical for rapid biological establishment and purification.

The second group of nitrifying bacteria to populate are those of Nitrobacter, which convert nitrite to nitrate. This period takes up to approximately twenty-one days, after which nitrite should be almost gone. During this phase, it is highly beneficial to perform additional partial water changes. Nitrite is also a very toxic compound. When present in high enough concentrations, it is lethal and can affect the red blood cells of fish. Should nitrite levels persist for more than twenty-one days, additional partial water changes should be performed, along with supplemental doses of Cycle.

It is important to understand that water chemistry, temperature, pollutants and other factors can affect the performance of nitrifying bacteria. Maintaining stable temperature, pH and water quality is important for all tank inhabitants, even for those that are invisible to the human eye, specifically, bacteria. Although ammonia and nitrite readings may be zero, after approximately one month, the aquarium has not reached full biological stability.

For new aquariums, ensure the following:

Regular removal of organic debris (dead plant leaves, etc.). Use Aqua Plus with all water changes (eliminates toxic elements and reduces stress). Regular dosage of Cycle (builds and maintains superior biological filtration).