Proper aeration is important in the aquarium to provide a natural exchange of gases at the water surface. Oxygen, which is beneficial, enters the aquarium from the air to the water, and carbon dioxide exits the aquarium from the water to the air.
Surface agitation is easily done with aeration, or pumping air into the water so that it forms bubbles. The bubbles rise to the surface and burst, thus breaking the surface tension.
One way of providing the necessary aeration in an aquarium is to use air stones connected to an air pump. The air stones can be made from wood or other highly porous materials. When air is forced in one end of the air stone by the pump, it is released as bubbles from the other end.