Air Pumps For Fish Tanks
An air pump is a common device used to introduce a stream of air into the aquarium.
Most modern air pumps use a vibrating diaphragm to force air through a small flexible tube or hose, called an airline. At the end of the airline (in the aquarium) an air stone or diffuser is attached which separates the stream of air into a number of fine bubbles.
The air pump sits outside the aquarium and if it is situated below the water level (e.g. in a cabinet under the tank) it should be fitted with a non-return valve to prevent water siphoning through the air line and out of the tank during a power cut.
Some water pumps also introduce air to the aquarium by using the water flow produced to 'pull' air in from above the water, and mix it with the flow of water; this is called a venturi.
Although an air pump is usually used to introduce oxygen, it is only the movement of the waters surface by the bubbles where oxygen enters the water. Because of this, a water pump placed near the surface is equally as good, and usually better, at introducing oxygen and has the added benefit that it can be used as a filter for little extra cost.
Extra introduction of oxygen, or an increase in gas exchange, can be beneficial when water quality deteriorates or when treatments or heavy planting uses up the aquariums oxygen.
In some situations, air pumps can be used to power filters such as under-gravel filters or box filters, which may have advantages over other types of filtration in certain situations.