Pumps come in two basic types: diaphragm and piston. The latter is cheaper, and adequate for smaller aquariums or small tank setups. It is the small pump usually found in aquarium kits, or sold with small aquariums. Larger diaphragm pumps can drive up to 5 or 6 aquariums. They are noisy and tend to wear out over time. Piston pumps are more powerful, reliable, longer lasting and come in sizes that make them practical for large fish rooms with many tanks.
Diaphragm pumps tend to vibrate, so they will skate around if they are not tied down.
Here are some tips for maintaining smaller diaphragm pumps.
Pumps should be place above the water line of your highest aquarium to prevent back-flow if the pump is shut off. If you must locate the pump below the water line, use air check valves. Small check-valves can be placed on individual air lines, or a large check valve can be placed near the pump. In the case where pumps use an ail filter, replace them or clean them to maximize air flow. If you use air stones, replace them or clean them regularly. Air stones cause the pump to work harder to force air through them. Make sure all connections between the pump and filter are tight. Diaphragms need to be replaced regularly to maximize air pressure. Rubber parts and flappers will also need to be replaced occasionally. Piston pumps are suitable for ten or more tanks. You should consider getting a pump rated for twice as many tanks as you think you will set up. If you use two filters in each aquarium (recommended), than you should get a pump rated for four times the number of tanks you think you will need. For example, the Hagen’s “The Pump” Model 80 is rated for 90 air stones. However it drives about 45 tanks with two filters and 3/4″ PVC piping.
Piston pumps tend to be quieter and more reliable than their cheaper alternatives. When you consider how important air is to the biological cycle of the tank, why compromise on cost in this area?