The methods of modern aquarism allow you to maintain the home of virtually all inhabitants of rivers, lakes and seas. The only exceptions are deep-sea animals, which need to ensure the monstrous pressure of the water column. And all this was made possible by improving the filtration of aquarium water.
Filtration is the purification of a liquid from small suspended particles as it passes through a filter. However, aquaria means by the word "filtration" a broader concept that includes water purification not only from all sorts of suspensions (mechanical filtration), but also from the waste products of aquatic organisms. The term “regeneration” is more suitable for this type of cleaning, but for simplicity we will agree to call both of them mechanical filtration and regeneration as filtering.
Filtering methods can be divided into three groups:
- Biological filtration. This is the purification of water during its circulation through a substrate inhabited by microorganisms that mineralize the dissolved waste products of the inhabitants of the aquarium.
- Mechanical filtering. In the simplest case, the biofilter combines mechanical and biological cleaning, but if that is not enough, then in the aquarium the water becomes cloudy due to the smallest suspended particles, which indicates the need for an additional mechanical filter.
- Chemical filtration. When it undesirable substances are absorbed by activated carbon or other absorbents, destroyed by ozone and ultraviolet radiation.
The biological filter consists of a substrate for bacteria and a system that provides continuous circulation through the substrate of purified water (Fig. 1). The substrate (1) is a layer of coarse sand with a fraction of 3 to 5 millimeters, a thickness of 7.5 centimeters or more, piled on a perforated surface (2), which is called false bottom.
Water is circulated by the so-called air-lift pump (3) due to the movement of air bubbles from the sprayer (4).
The first two weeks after the launch of the biofilter heterotrophic bacteria thrive and the concentration of ammonium in the water increases sharply, which can be detrimental to aquatic inhabitants. This unpleasant phenomenon is called the "syndrome of the new aquarium". To avoid danger, delicate fish species inhabit the aquarium only a month after the launch of the biofilter system.
As the nutrient medium appears in the substrate, nitrifying bacteria begin to develop and reach a maximum in the third or fourth week. the concentration of nitrite, which is also, despite the decrease in the concentration of ammonium, is dangerous for residents of the aquarium. In turn, bacteria that consume nitrites gradually reduce their concentration, and the biofilter begins to function normally.
The process of biological filtration usually takes about two months. It can be somewhat accelerated using a small amount of gravel from an old, safely operating filter. Having added some ammonia to the water (not to be confused with ammonia), it is possible to speed up the formation of the bacteriofauna of the filter for about a week.
Usually, to form the fauna of the biofilter, enduring species of fish, such as Blanius and scorpions, are planted in an aquarium, and the bee-eater is sown in a freshwater one. These inhabitants easily tolerate near-fatal ammonium doses. They feed the fish abundantly, thereby activating the metabolism. When the ammonium and nitrite maxima pass, they gradually begin to fill the aquarium with the inhabitants for which it is intended.
As shown by domestic and foreign experience, the substrate thickness of 7.5 centimeters is most optimal. With a smaller thickness, it is more difficult to obtain a uniform flow of water washing the sand particles with bacterial films located on their surface. As a result, "dead" oxygen-free zones may appear in the aquarium, in which hydrogen sulfide is formed under the action of anaerobic bacteria. With an increase in the thickness of the substrate, the resistance of the circulating water increases sharply.
A prerequisite for the normal operation of a biofilter is its oxygen regime: the oxygen content in water must be close to saturation.
From an aesthetic point of view, a thick layer of soil, which is a biofilter substrate, especially in small aquariums, is not attractive. Therefore, another biofilter layout is often used — in a vertical design, along the back or side walls of the aquarium, and also to take it out of the aquarium in general. For freshwater aquariums of a small size, a layer of synthetic cotton (nylon, polyester) is used, measuring a centimeter and a half, on which a small three to four centimeter layer of gravel is located (Fig. 2).
The next stage in the evolution of the filtration system is the separation of mechanical and biological filters (Fig. 3). At the same time, in order to remove organic residues from under the false, the direction of water circulation is changed. Water that has already been de-suspended by a mechanical filter (2) is pumped under a foulind.
Every hour, at a minimum, the entire volume of aquarium water must pass through the biofilter. But it is better if the capacity of the circulating pump is two to three times greater, for example, for an aquarium of 100 liters it is better to have a water pump of 200-300 liters per hour.
There are systems of biofilters (Fig. 4) in which the substrate is irrigated with water, then by gravity returning to the aquarium. These systems are very effective, they saturate the water well with oxygen, but in them, due to active evaporation, the water flow increases, causing the density in the saltwater aquarium.
It should be noted that there is no fundamental difference in the filtration systems of the freshwater and saltwater aquarium. Simply, many inhabitants of a freshwater aquarium are not so sensitive to water pollution and its quality, so water purification with a mechanical filter and its periodic replacement often allow us to solve the problems of a safe aquarium without a biofilter.
In fig. 5 shows the construction of a simple and convenient mechanical filter. Here, the filtering material (kapron, nylon, polyester thread) is recommended to be washed at least once a week to avoid excessive water contamination.
The most effective in chemical filtration is an adsorption filter with activated carbon, which is often called a carbon contactor. The device of a coal contactor is similar to a mechanical filter and differs only in that it does not use synthetic fiber, but activated carbon, best of all birch, previously boiled and washed from coal dust.
Usually a carbon filter is used in a periodic mode when a yellowish color appears in the water — in freshwater — and yellowish-green — in a saltwater aquarium. Such a filter removes water-coloring organics, which is beyond the power of the biofilter.