An airpump’s primary role is to provide additional circulation and to disturb the water surface creating a larger area for oxygen exchange as described in the aeration section, (not to mystically force air into the water as is often thought) but this is not the limit to their use.

An airpump is ideal for powering sponge and box filters in breeding aquariums or under gravel filters where a motorised power filter would produce too much turbulence. They can also be used to provide agitation for a brine shrimp hatchery and to drive off chlorine from tap water.

Airpumps are available in a wide range of sizes describing their flow rate. This refers to the volume of air it produces in a given time, usually measured litres per hour (lph). Some more expensive pumps also have regulators that allow the flow rate to be varied. It is worth considering weather this feature is worth the additional expense as in my experience pumps are generally run at their fullest output.

The biggest complaint about an airpump is the constant humming caused by the vibrating bladder within the unit. Manufactures have however realised that quiet pumps sell and have thus incorporated many sound reducing measures in their design. Sometimes manufactures state the noise level (measured in decibels dB) in the technical specification on the box. The lower the figure the quieter the pump. The quietest pumps have rating of 30 decibels or less. At least one manufacture has tried to reduce noise by removing the cause, the bladder, and replacing it with a piston mechanism, which produces a gentle chuffing sound. Should the noise of an airpump really drive you mad, I know of some aquarists who put the pump in an adjoining room and run the airline through the wall. Never muffle an airpump by placing it in a box or wrapping it in a towel as these methods can cause the pump to over heat.

Remember when positioning an airpump it should be above water level. The reason for this is that if the pump fails, water will back siphon along the airline emptying the aquarium. If the pump must be sited below the aquarium a non-return valve (check valve) should be fitted although this can reduce the efficiency of the pump.

Some methods for maximising your pump's output are: -

• Keep runs of airline as short as possible.
• Place the pump above water level to avoid using an airline non-return valve (check valve).
• Keep runs of airline free from kinks and avoid using any connectors, taps, etc.
• Regularly replace airstones. They clog and cause back-pressure.
• Check and replace airpump bladders and filters periodically.