Aquarium Air Pumps
The advantages of aeration of water are twofold. First, it is helpful in ridding the water of the harmful carbon dioxide which, when allowed to accumulate, has such a detrimental effect on most fish. Second, it serves the very useful purpose of aiding in the circulation of the water, thus ensuring a more even distribution of heat.
The mechanism for the supply of air is the commercial air pump, of which several different types are available to the aquarist. In the piston type of pump, air is compressed and forced through the air lines, usually plastic tubing, to run the air stones or filters. The piston-type pump has two cycles, the compression stroke and the intake stroke. When the piston is pushed down into the cylinder, the air is compressed, thus the compression stroke. When the piston is raised up, it sucks in air by creating a vacuum in the cylinder. The cylinder is fitted with a valve that is closed during the compression stroke and open to admit air during the intake stroke.
Another type of pump is the vibrating-membrane type. A rubber membrane that vibrates quite rapidly takes the place of the cylinder-piston arrangement just described. Most of the vibrating-membrane type pumps have lower capacities than do the piston types. The rubber membranes need replacing after a period of six months to a year, and there is a definite air loss when slight cracks develop in the rubber membrane because of the incessant vibration. Most manufacturers have facilities for the replacement of these parts and it is the wisest policy to return the pumps to the manufacturer for adjustment and repair. The cost is usually trivial, so don't try to replace the membrane yourself!
The air pressure built up by most vibrating-membrane pumps runs between 3 and 6 pounds per square inch. Naturally, the greater the pressure the greater the number of outlets the pump can maintain.
In general, insofar as price alone is concerned, the cheaper pumps are vibrating-membrane types. The principal objection to this type of pump is the noise that it makes. It has the advantages of being cheaper to buy, cheaper to operate, and it is usually sufficient for two to three small tanks.
The proper arrangement of air stones, filters, and escape valve is most important in utilizing the full capacity of the pump.
Not all appliances give the wattage. All, however, must give enough information so that wattage can be easily figured out.
Some things to look for in a good pump are: low wattage (less than 40 watts), a year's guarantee, easy to repair, easy to lubricate, static free (equipped with a condenser), beltless, replaceable rings for pistons (felt or leather being best), noiseless, and great output (in cubic inches of air).
