Pumps and Water Circulation

The Importance of Aeration
Maintaining good water circulation in an aquarium is essential to the health of fish and aquatic plants. The movement of water in an aquarium ensures that more water will reach the tank surface and be exposed to air. When water is exposed to air, an exchange of gases takes place between the two -- the water releases carbon dioxide into the air, and in return, oxygen from the air is absorbed by the water.

This exchange of gases is essential for sustaining life inside the aquarium. If carbon dioxide isn’t released, the fish in a tank will be poisoned -- and if new oxygen isn’t absorbed by the water, the fish will "suffocate." The process through which this critical gas exchange takes place is called "aeration."

In most aquariums, aeration is achieved by using air pumps or water pumps -- or a combination of the two.

How Air Pumps Work
Electrically-driven air pumps produce compressed air that is typically used to do two things, both of which help to aerate tank water:

Operate aquarium filtration systems. (See "Filtration")

Release a large volume of air bubbles into the aquarium.

By operating filtration systems, an air pump increases the circulation of water throughout the tank. (Most filtration systems take in water from one part of the tank, and put it back in another.) As a result of this constant circulation, water from different sections of the tank is always rising to the surface to exchange its carbon dioxide for oxygen.

Air pumps release their air bubbles through a block of porous material call an air stone. (The two are connected by a plastic air tube.) Since air bubbles are lighter than water, they rise to the surface of the tank. As they rise, the bubbles carry streams of tank water with them. When this water is exposed to air at the tank surface, the life-sustaining gas exchange takes place. Without this aeration, water at the bottom of a tank can become too oxygen-deficient to support healthy fish life.

Smaller bubbles are more efficient at aerating an aquarium, since they carry more water with them than large bubbles as they rise to the surface. The small holes in air stones will become clogged and need an occasional cleaning with hot water and a brush. Never use soap to clean an air stone or air tube.

There are two types of air pumps: the vibrator/diaphragm pump, and the rotary valve pump. A single air pump can power a filter and air stone if an adapter is installed on the unit. When choosing an air pump, consider more than the size of the tank. If you want to operate an undergravel filter and air stones from an air pump in a 10-gallon tank, you will need a larger unit than someone who only wants to create bubbles in a 30-gallon aquarium.

A non-return valve added to a pump will allow it to be installed under the water’s surface, without worrying about water siphoning back into the pump.

Much more powerful than air pumps, water pumps push water upward in the aquarium tank at a rate that is a lot faster than air bubbles can rise through water. The result is much more vigorous water circulation, and greater aeration.

Water pumps are very useful in larger tanks, marine aquariums and reef systems. However, in smaller tanks and tanks stocked with fish that do best in calm waters, the standard air pump may still be the preferred choice.

There are a wide variety of water pumps designed for different purposes. In addition to circulating water themselves, water pumps are used to run filtration systems and larger protein skimmers.

Many filtration systems have their own built-in water pumps. When operating filtration systems, water pumps also aerate tanks by increasing water circulation.

Spray bars will often be installed on water pumps to direct water over a larger area and increase the level of aeration even further.

Power heads are the simplest water pumps, and they are often used to increase the rate at which water flows through filtration systems, especially undergravel filters.

Different water pump models can be positioned inside or outside the aquarium. Outside-the-tank models must be primed first by having water placed in them before they are started. All water pumps and power heads are centrifugal pumps that must be placed below the water to operate, since they can only "push" water up, and cannot "pull" it up through tank water.

Regular maintenance is critical to the efficiency of water pumps. The screen plates or filters that keep debris away from the pump’s impeller should be removed and cleaned. Impellers must be cleaned every three months.

To avoid severe damage, never run water pumps "dry" (without water running through them).