Biological filters are used in aquaculture and aquariums to remove ammonia (under aerobic conditions) or nitrates (in anoxic conditions or lack of oxygen in the water).


The ammonia nitrogen or ammonia in the water (TAN: total ammonia nitrogen) is a highly toxic compound formed as a result of the physiological activity of organisms and the decomposition of protein material present in the water.

The rate at which ammonia nitrogen is in the water in ionized form (NH4 +) or non-ionized (NH3), depends on the pH and water temperature. The non-ionized form is extremely toxic for fish.  With increasing pH and temperature, the compound NH3  is the most abundant in the water. Ammonia produces adverse effects in fish from 0.3 ppm and therefore should be removed from the system following the natural process known as nitrification.

In the nitrifiers aerobic filters, a group of bacteria transforms the ammonia present in the water in two-stages (in both NH3 and NH4+) into nitrate, less toxic than ammonia (levels of 400 ppm have been registered without causing any disturbance in fish).


It is important that the nitrification reaction is fully developed to avoid the presence of the nitrite ion (NO2-), which is an intermediate product in the reaction, which itself can cause problems from concentrations of 2.7 ppm.

To do this we must ensure that:
- sufficient oxygen in the water.
- the water is in contact with the bacteria long enough for the reaction to complete.

Chemical reactions of nitrification:

NH4+ + 1.5 O2 → NO2- + 2H+ + H2O (Step 1: conversion of ammonium to nitrite)

NO2- + 0.5 O2  → NO3- (Stage 2: conversion of nitrite to nitrate)




To remove nitrates from water (denitrification) requires the use of a sealed biological filter, ensuring that there is no presence of oxygen in the water, so that denitrifying bacteria can develop properly. In this case, nitrate (NO3-), which can be inconvenient in some aquariums, is transformed into nitrogen gas (N2), that is removed by aeration. For this transformation to be successful, you need a supply of carbon (as methanol) to be introduced in sufficient quantity.






The placing in service of a biological filter requires an initial activation process. You should wait until the bacterial colony is installed in the filter media to start operating the biological filter. This requires some time that could be longer or shorter depending on the management and condition in which the filter is.

The process of colonization is a natural process, if the water has certain amounts of ammonium, the colonies of nitrifying bacteria will grow eventually in the biofilter. There are started colonies in the market that can be placed in the filter to accelerate the process of colonization. Other mechanisms include the use of filter media from another filter installation already in operation.

The filter efficiency also depends on the nitrifying biological filter media used. The greater the surface area of the environment the greater the level of ammonia removed.



In INNOVAQUA we are specialists in the calculation of biological filtration that suits the specific needs of each facility, both in the choice of filter as in the biological material for bedding.





Filter type: Percolating filter



The percolating filter is a gravitational open filter, where there is a perfect contact between water, air and filter media. Thanks to the rotary spray system, the water is distributed evenly throughout the filter section and falls freely across wetting the filtering surface, taking full advantage of the filter media volume. The side entries of the percolating filter are aerators that through natural convection improve the oxygenation of all filtering bedding. That is why, this is a system with no restriction of oxygen, but does not keep the recirculation pressure








Filter type: Pressurized filter


The pressurized biological filter works very similar to the sand filter. The flow may be upward or downward as both collectors and diffusers have the same morphology and there is no danger of coming into the pipes. For closed filters it is recommended to use high density filter material, since these materials do not float in the water, and a bigger volume of filter can may be used. These filters retain the pressure in the recirculation system but instead oxygen may become limited and reduce the capacity slightly. Efficiency can be increased by an extra supply of oxygen to the water.








Fluidized bed filter


Fluidized bed filter is an open filter where a permanent water flow provides the contact between water, air and filter media that is continuously moving, sometimes in needed a supply of oxygen to increase performance. The water returns to the circuit by gravity so it is necessary to design correctly the dimensions of the filter tank.

When the filter is very large circulators equipment is  incorporating  for assisting the movement of the media.









Plastic Material for bacterial bed BIOMEDIA INNOVAQUA

- High surface area.

- Suitable for all types of biological filters.

- High strength and very flexible.

- Suitable for use with fresh water and sea water.