Biological filtration

 

Biological filtration is an essential part of aquarium maintenance and plays a crucial role in the health of the aquarium inhabitants. It refers to the process by which beneficial bacteria convert harmful waste products into less harmful compounds. This process is essential to maintain a healthy and stable ecosystem in the aquarium.

Why is biological filtration important?

Degradation of ammonia

Fish and other aquarium inhabitants constantly produce waste products containing ammonia (NH3). Even in low concentrations, ammonia is very toxic to fish and can lead to stress, illness and even death.

Conversion of nitrite

Ammonia is converted into nitrite (NO2-) by nitrifying bacteria of the genus Nitrosomonas. Nitrite is also toxic to fish and can impair oxygen transport in the blood

Conversion of nitrate

Another set of nitrifying bacteria, mainly of the genus Nitrobacter, converts nitrite into nitrate (NO3-). Nitrate is much less toxic compared to ammonia and nitrite, but can accumulate in high concentrations and affect plant growth and promote algae growth.

The role of beneficial bacteria

In an aquarium, beneficial bacteria mainly colonize the surfaces of the filter, substrate (substrate) and other decorations. There are two main types of bacteria that are responsible for biological filtration

Nitrosomonas

These bacteria oxidize ammonia to nitrite.

Nitrobacter

These bacteria oxidize nitrite to nitrate

The nitrogen cycle in the aquarium

The biological filter process is part of the nitrogen cycle in the aquarium

Ammonia production

Fish excrete ammonia, which also comes from the decomposition of food residues and dead plant material.

Nitrification

Nitrosomonas bacteria convert ammonia into nitrite, and Nitrobacter bacteria convert nitrite into nitrate.

Denitrification (optional)

In special filter systems or in a deep sand bed, nitrate can be converted into gaseous nitrogen (N2) by anaerobic bacteria and removed from the water.

Setting up and maintaining the biological filter

Establishment of the bacterial colonies

When starting up a new aquarium, it usually takes a few weeks for stable bacterial colonies to form. It is important to populate the aquarium slowly during this time and to check the water values regularly.

Care of the filter

Mechanical cleaning of the filter should be carried out carefully so as not to disturb the beneficial bacteria too much. The filter media should be rinsed in removed aquarium water and not under tap water, as chlorine can kill the bacteria.

Maintaining the balance

Regular water changes and checking the water quality help to control the load of pollutants and maintain a stable biological balance.