The purpose of the biofilter is mechanical, chemical, as well as biological purification of water in the aquarium. As a rule, speaking of biofilters, imply large canister filters. It should be noted that the design of the canister filter involves a large surface of the filtering medium. In this article we will talk about the processes of biofiltration, which occur in Fish Tank Filters, as well as the effect of the Fish Tank Filter device itself on the biofiltration passing in it.
Fish Tank Filters are divided into internal and external, while in the aquarium external filters are often called canister filters or biofilters. Aquarium external filters are called biofilters, because their large volume in comparison with internal filters makes it possible to place in them a large volume of various filtering fillers, as well as various additional devices and devices that improve the quality of biological and mechanical filtration of water in aquariums. Given this fact, the aquarium external filters are often called biofilters, although biofiltration also occurs in other filters for aquariums, as well as aquarium soil.
Purification of water in the aquarium is divided into biological and mechanical. Under mechanical cleaning implies the purification of water from mechanical suspension, i.e. water purification from sand, dirt, elements of organic remains, etc. Biological water purification involves the processing of organic matter, which is contained in the water and is carried out with the help of beneficial bacteria. It will be about the biological treatment of aquarium water.
For the biofiltration process to work properly, oxygen is needed, dissolved in water, which is required by bacteria. Oxygen is taken from bacteria from the water that passes through the filter, but when the filter is turned off, the water supply stops and the colony of bacteria dies from asphyxiation without oxygen. Biofiltration proceeds as follows: Organic matter, which is part of most aquarium waste, during decomposition increases the concentration of ammonium / ammonia, then the ammonium / ammonia transition occurs first to nitrite and then to nitrate. Of course, the process is actually more complicated, however, in this article its detailed description is simply meaningless, and aquarists generally adhere to the general designated only provisions. The essence of the biofiltration process described above is that harmful for aquarium fish waste is converted to less toxic forms. The end point of the transformation in this case is nitrates. Of all the 3 elements listed above, they are safer for fish. Usually, the removal of nitrates occurs along with the next water change in the aquarium.
Now we should consider the structural features of biofilters. Many canister (external) filters, namely, we are now considering, are usually divided into three or more compartments through which water passes during the biofiltration process. The arrangement and role of such compartments has become almost universally accepted standard:
Compartment with ceramic rings. As a rule, water flows through this compartment first. Ceramic rings break the flow of water passing through them, with a more even distribution, and also carry out a primary, coarse mechanical cleaning, screening out large organic matter and other debris.
Then it is usually carried out the installation of a compartment filled with “bio-spheres” or other filler with a larger surface area and a finely porous structure. Such a filler is home to a larger number of beneficial bacteria with which biofiltration is performed.
Usually, after this installation of the compartment with the “fine cleaning” filler is performed. Basically, such a filler is 1 or more sponges, in some cases with different pore structure and size. In addition to sponges, often in such a compartment is placed activated carbon, which serves for additional water purification. But coal has a limited duration, it is necessary to replace it; therefore, aquarists often use it only as a temporary filler. At this stage, water is cleaned from residual matter, as well as debris present in the water at that time.
This scheme is typical of many canister (external) filters, which are now widely distributed. Of course, the differences may be, but the general principle remains the same. Often, differences are reduced to the size and shape of compartments of biofilters, methods of their maintenance, loading, as well as differences between fillers, designed to perform the same actions. In addition, the number of compartments may be smaller and larger. Additional compartments are filled with an additional volume of conventional fillers or used to load non-standard fillers, for example, to load a bag with chemical reagents that neutralize nitrite, ammonium, ammonia, etc.
It is also worth noting that in recent years there are filters on the market with built-in, additional equipment, such as an aerator, aquarium heater, UV sterilizer, etc. So far these filters have not spread widely, but they are still worth mentioning.
This could complete the description of the canister (external) Fish Tank Filter, but I would like to mention the mode of operation of the biofilter (both internal and external). For Fish Tank Filters (or rather, for bacteria living in the filter) a constant supply of oxygen is required, and when the filter is turned off, oxygen supply stops. This means that the beneficial bacteria will die of suffocation after the total oxygen supply has been consumed, and it will take a long time to restore the colony of such bacteria. In addition, the dead bacteria form biomass, which, when the filter is turned on, enters the aquarium poisoning the water with harmful compounds. As a result, we can draw the following conclusion: the operation of the Fish Tank Filter should be done around the clock. In work the maximum break should be no more than 15-20 minutes. With a long simple filter, it is necessary to thoroughly wash the filtering fillers and the filter itself, and after switching on, it is worth considering that the beneficial bacteria recover after a time (from several days to two or three weeks).