What Bacteria Form Inside of a Fish Tank?

Different species of bacteria convert the metabolic waste of fish into harmless substances. Both nitrifying and denitrifying bacteria cultures are present in aquariums and more specifically, within the filters of these aquariums. These bacteria cultures are sessile and need to coat different suitable surfaces, as opposed to swimming in the water. Both types of bacteria form cultures on the substrate and décor items, such as driftwood and rocks, but are most abundant in the biological material in the aquarium's filters. Although these bacterial strains create a balanced and healthy environment in the aquarium, they have their own specific requirements as well.

  1. Nitrifying Bacteria

    • The nitrification process is the conversion of ammonia (NH3) to nitrites (NO2-) and the further conversion of NO2- to nitrates (NO3-). Nitrifying bacteria -- which require an oxygen-rich environment in which to function -- are responsible for this process. Nitrosomonas and nitrobacter are the two strains most commonly found in aquarium environments. Nitrifying bacteria thrive when oxygen levels are at 80 percent saturation. These bacterial strains also grow best in water with a temperature in between 77 to 86 degrees Fahrenheit. Nitrifying bacteria are sensitive to chlorine in tap water and to certain aquarium medications.

    Denitrifying Bacteria

    • Denitrifying bacteria convert NO3- to nitrogen gas (N2). These bacteria are heterotrophic and function using organic carbon or hydrogen as an electron donor and nitrate as the electron acceptor. The hydrogen or organic carbon is oxidized to water or carbon dioxide and the NO3- is reduced to N2, which leaves the aquarium via the surface water. Denitrifying bacteria can only survive in an oxygen poor environment and require a special biological material within the filter compartment, in which to grow.

    Culture Material for Nitrifying Bacteria

    • Nitrifying bacteria require a large surface area on which to grow. These cultures must be exposed to aquarium water, which is carrying the molecules of metabolic waste and need to be exposed to high oxygen levels. Ceramic media, which has been designed for aquarium use, is a very suitable biological filter material, as it contains an adequate surface area, on which the bacteria can grow. The colonies of nitrifying bacteria are sticky and are not flushed off the media, as the water flows over it.

    Culture Material for Denitrifying Bacteria

    • Denitrifying bacteria can only survive in an oxygen-depleted environment. The ceramic filter media, which is used to culture nitrifying bacteria, is equally suitable for denitrifying bacteria, as these ceramic tubes are riddled with holes. While the oxygen loving nitrifying bacteria strains grow on the outer surface, which is exposed to water movement and oxygen, the denitrifying strains settle deep in the holes, where water and oxygen cannot easily reach.