Applications of air pumps in aquarium filtration systems

Aquarium air pumps are designed to pump water over a filtration system and remove any solid waste. They were originally used to power under-gravel filters, but this type of filter has lost its previous popularity in favor of newer more powerful types. However, some people still use nothing else. Are they just traditionalists, or do they know something the rest of us should?

Air pumps are now used more to power corner filters and sponge filters, and in salt water aquarium to power protein skimmers. Air pumps are also used for aeration through devices such as air stones and to provide the water movement and currents that some fish prefer. The main advantage of air filtration is that it does not involve much power, and it is better and safer for the smaller fish. Strong water currents tend to stress delicate fish, and smaller fish can be drawn into the water intakes of powerful electric water pumps.

The pump is positioned outside the tank, but as close to it as possible so as to minimize energy loss through excessive lengths of tubing. It's not as popular as a water pump, but is useful for smaller tanks with small fish. The power of the pump will depend largely on the capacity of your tank, as well as on the design and number of any aeration devices you wish it to power. However, if you are using your pump with an under-gravel filtration system, then you will need a more powerful pump than otherwise.

An under-gravel filter consists of a perforated plate covering the entire area of the aquarium, and is fitted close to the bottom. It is then covered completely by gravel. One or two 'uplift tubes' are attached to the plate, and rise into the body of the aquarium. These contain an air stone that is fed by an air line from the air pump that generate a stream of air bubbles that push the water before them. As the water is pushed up by the bubbles, this creates a potential vacuum that draws more water up through the uplift tube.

In order to replace this, water is drawn through the gravel and hence filtered. In addition to mechanical filtration the gravel also contains friendly bacteria that purify the water by breaking down harmful ammonia into nitrates. In this way, there is a gentle circulation of water through the gravel, under the perforated plate, up the uplift tube and back into the body of the tank. All of this is driven by a stream of air bubbles provided by the air pump.

Another filter that is air driven is the corner, or box filter. These are filled with filter media such as activated charcoal and again the air pump creates a flow of water by means of air bubbles. These filters are not suitable for use as a permanent filtration system in large tanks, but for use in emergency or in breeding tanks, they are fine.

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