Water & Air Pumps
Pumps, including powerheads, serve two major functions: creating currents and aerating, and moving water through various peripherals like sumps, filters, skimmers, etc. They are also used as wavemakers in reef tanks.
- Moving water creates aeration by constantly mixing the surface with the rest of the water. Pumps move much more water than airstones can, and thus they provide greater aeration, despite the fact that no bubbles may be produced.
- Many species of fish will not thrive without proper current in the tank. In addition, currents prevent detritus from accumulating.
- When devices are located outside the aquarium, one or more pumps are needed to move the water through a circuit that goes from the tank to the peripherals and back. Gravity can be used for part of the circuit, but at least one pump is needed.
- In power filters the integral water pump usually pumps water from the tank into the filter, from which it returns by gravity, while in canisters the water normally drains by gravity into the canister, from which it is pumped back to the tank.
- Many marine invertebrates rely on the pulsing currents of breaking waves to keep them free from settled debris and to bring them food.
- Riverine animals are adapted to a strong current that flows in one direction, but reef animals are adapted to alternating currents.
- Revolving pumps oscillate much like a fan, varying the flow direction constantly.
- Timers utilize two or more pumps, turning them on and off in sequence, to deliver pulses of current from different directions.
- Surge devices pump water to a vessel above the aquarium, which periodically releases the accumulated water in one powerful dump, effectively mimicking wave action.
Choosing a Pump
- The first factor in determining what pump you need is the volume of water you need moved. If you are running a filter or skimmer, it will be rated for a certain volume of water per hour. Generally a turnover of about 6 gallons per hour is recommended for most filtration; thus, if you have a 40-gallon tank, use a pump that moves about 240 gallons per hour.
- Remember to take the head into account. This is the height the water has to be pumped against gravity. While minimal for hang-on filters, it can be considerable for a canister system—often several feet from the floor to the top rim of the aquarium. Output volume drops off extremely quickly as head increases, and only the most powerful units can handle more than a few feet at reasonable flow rates.
- Because it is much more corrosive, salt water requires that all pump parts in contact with water be highly corrosion-resistant. A pump rated for salt water can be used for fresh, but the reverse is not true.
There are two reasons people use air pumps. The first is that they are using an air-driven filter. Inside box filters and sponge filters use air to move water through the filter. The second is that people like bubbles. In fact, for some aquarists, a tank isn’t right unless there is at least one stream of bubbles rising in it. A side effect of both of these uses is that the current created by bubbles rising in an aquarium contributes to the aeration of the water. You certainly don’t need an air pump, since despite the name “aeration,” air bubbles are not necessary or even basic to gas exchange, but you certainly can use air for aeration.
- Electric air pumps create a stream of air under pressure. Pressure is not the same as volume. The volume of air pumped out determines how many air-driven devices can be run by the pump provided pressure concerns are kept equal.
- The resistance posed by an air-driven device determines the pressure needed to run it. Airstones create more resistance than an open tube, so on a given pump you can run more undergravel filters that simply have air tubing run to each riser tube than those that use an airstone in each riser. Also, the deeper the water, the greater the resistance. A pump capable of running several devices in a 12-inch-deep aquarium might not be able to run even one in a 24-inch-deep tank.
A few simple precautions will get you maximum performance from your pump.
- If your pump has more than one outlet, use a valve or a tee to combine their output. This assures that the backpressure on each diaphragm is equal, which prevents uneven wear and early failure.
- Place a check valve between the pump and the aquarium. It permits air to flow into the outlets in the aquarium, but it prevents water from siphoning back from the tank into the pump in the event of a power failure or in case the airline gets disconnected from the pump.