The filters in the aquarium operate using either electric pumps or air flow, using the airlift principle. Filters of the second type are much cheaper. Most newcomers who have recently become fascinated with hobbies such as aquarism tend to overvalue the amount of filtration required to maintain good water quality. However, veterans, who began to engage in aquarism even in those times when only a few could afford to buy an electric filter, know that the simplest filtration, which works thanks to the air, is quite capable of biologically treating a very large amount of waste. The only task that such systems can sometimes not cope with is the mechanical collection of all solid waste and the maintenance of water transparency.
The main parameters of the filter are the volume of the filtering medium and capacity (the rate at which water is pumped through the filter). Electric filters typically have a fixed capacity, for example 300 liters per hour (l / h). It is very important to choose a filter suitable for your aquarium in terms of parameters such as the size of the aquarium (the amount of water to be filtered), the load (the amount of waste treated) and the nature of the water movement preferred by the inhabitants of the aquarium. Immediately make a reservation that the power and size of the filter are not convincing evidence of the universality of its work for all types of aquariums. Excessive volume of filtering medium, of course, does not hurt, but too high speed of the flow of water can cause considerable discomfort and stress in fish. If the rate of flow of water is too high, it will be difficult for them to swim against the current. Small fish, especially fry, can be sucked into the filter and they will die. A filter with a capacity of 300 l / h in two hours will completely pass through all the water in a 600-liter aquarium, but in a 50-liter aquarium it will take only ten minutes. From the point of view of fish, this is about the same thing as living in a washing machine.
On the other hand, an insufficient rate of flow of water through the filter can cause the water to become turbid, and an insufficient volume of filtering medium will cause the filter to quickly become clogged, and it will be necessary to clean it too often. A decrease in the biological effectiveness of a filter can be the result of the death of a colony of bacteria living in it. A clear advantage has a filter with adjustable flow rate of water. All airflow activated filters can be adjusted by changing the air supply. Some (but not all) electrical filters have a flow rate regulator. They are more flexible and can be used in different aquariums for different types of fish – depending on how the aquarist’s interests develop or change.
Below are the types of filters that are most often found in the trade network:
• External suspended filter (waterfall) is a plastic box, sometimes consisting of several sections. It is placed on the outside of the aquarium. Such a filter may be driven by a centrifugal pump or air flow. In Europe, it is no longer popular, but it is often used in the United States, where very sophisticated electrical models of such a filter are on sale. Water can be fed into the filter from the aquarium, and then, after passing through the filter materials, to flow back into the aquarium. Another option is that water is pumped out of the aquarium using a pump, and then it flows back through a drain located above the water level.
• Air lift filter. It is a small plastic container, usually in the shape of a cube, a triangular pyramid, or a vertical cylinder. In any case, it works on the principle of airlift. Water usually enters the filter through a perforated cover, then passes from the top down through the filter material, and then rises along the airlift and goes outside. More recently, these filters were very popular. At that time, the only alternative was primitive, often leaking external boxes or expensive electrical external filters (canisters). But now they are mostly supplanted by other types of filters. Air-lift filters can still be used in small aquariums or to provide additional or short-term chemical filtration.
• The external filter canister is most often found in the form of a vertical cylindrical container (sometimes it has the shape of a rectangular box) for the filtering medium. On top is an electric pump. Water flows from the aquarium through flexible plastic hoses, and is pumped back again after passing through filter materials. Sometimes a flute tube is attached to the outlet – a rigid plastic tube with holes dissecting the water returning to the aquarium. It can be placed both above the water surface and in the water. Such filters of different volume and performance are commercially available (the latter can be adjusted in most models). Usually canister filters are not suitable for small aquariums.
• The internal filter cup is a plastic bottle with perforated side walls or water inlet slots. It contains filter media (usually one or more sponge cartridges). Above the balloon is an electric pump. All this device is immersed in water. Filters of various sizes are available, some of which have performance regulators. Such a filter should not be used in spawning aquariums, because it may well suck fry.
• "Head". This is a separate electric centrifugal pump, designed so that it can be connected to the filtering system, mainly to the bottom filter, which is under a layer of gravel. Some types of such pumps allow you to adjust the flow rate of water. Most of them are too powerful, so they should not be used in small aquariums.
• Foam separator. The operation of this device is based on an air cleaning process. At the same time, proteins and other pollutants are captured by air bubbles and transferred to the upper part of the device, where they accumulate in the form of foam in a removable bowl. Best of all the column works in salt water. Freshwater models are inefficient and do not bring any real benefit.
• The sponge filter is one of the very first and primitive designs of air-lift filters. Nevertheless, they are still popular and are most widely used in spawning. This filter consists of a perforated plastic tube on which one or more sponge cartridges are attached. Air passes through the tube and carries water with it. Water containing waste passes through a sponge filter and flows into the tube. Many aquarists constantly make the sponge filter work somewhere in the corner of the common aquarium, thereby maintaining the biological maturity of the sponge, so that later, when necessary, use the filter in a quarantine or spawning aquarium.
• The jet filter consists of one or more perforated trays with filter material placed one above the other above the aquarium. Water, returning from the external filter canister, is sprayed (usually with the help of a “flute” divider) and gets onto the filtering material in the upper tray. It then flows in streams through it, flows down onto the trays lying below and eventually ends up in the aquarium. The advantage of this type of filter is a good saturation of water with oxygen, leading to optimal biological processes. Even using only one tray creates a good way of spraying water returning from an external filter, and reducing turbulence in the aquarium. In addition, it is an excellent technique for ensuring a high oxygen content in the water.
• Bottom filter (false bottom). This is a bottom filter consisting of a perforated plastic plate, which is placed on the bottom of the aquarium under the ground. The filter plate is connected to one or more lifting tubes that rise above the ground layer. They usually end on or near the surface of the water. The soil in this case acts as a filtering medium (filtering layer). For optimum efficiency, the filter layer should have a thickness of 6.0-7.5 cm and a grain size of 4-5 mm. Such filters can operate on the principle of direct flow or reverse flow. In the first case, water flows down through the layer of gravel, and then rises up through the lifting tube. In the second case, water is pumped down the tube, and then it rises, passing through a layer of substrate. The direct flow is driven by air flow or a “head”, and sometimes by an external filter, the outlet tube of which is inserted into the bottom tube of the bottom filter. The forward flow is driven by a “head” operating in the reverse mode (not all models can do this) or by an external filter, the output tube of which is inserted into the bottom filter tube of the bottom filter.
The advantage of conventional flow is that the “inlet” is the entire surface of the soil, so that all solid particles are captured during the filtration process. However, in the end, this leads to substrate contamination with neutral residues (and not hazardous waste, as many aquarists believe). Through return flow, driven by a canister pump, solid particles are mechanically drawn into the external filter, and the substrate acts primarily as a biological filter. Although, in all likelihood, the process of biological filtration occurs mainly in the canister, where the waste is split. As for the reverse, it is difficult to find any potential advantage of it. It is impossible to start the bottom filter with very fast flow of water, as it usually leads to the absorption of particles through the filtering layer and ascent upwards through the lifting tubes (in the case of a normal flow) or leaching from the soil (in the case of a reverse flow).