Aeration is used primarily for oxygenation but may also be used for mixing of water volumes. The efficiency of bubble diffusers will depend largely on two factors:
- The size of the bubbles that are liberated - the smaller the bubble, the higher the surface area to volume ratio, and the more efficient the gas transfer.
- The contact time that the bubble has with the water - i.e. the depth that the bubbles are injected into the water column.
A medium sized air bubble of 3mm will rise at a rate of 1ft/sec, therefore a bubble released from a depth of 3 ft will have a contact time of 3 seconds. Air injected at depths greater than 4 ft can lead to excess nitrogen dissolving in the water, which can in turn result in what is commonly known as air bubble disease.
Smaller bubbles can be created using air stones with smaller pore sizes. However, with this reduction in pore size comes an increase in the pressure required to produce the bubbles. Smaller pore size diffusers also have a greater tendency to become blocked. This can occur through dust from the air inflow, the formation of calcium carbonate (especially in saltwater or hard water set ups) and through a build up of bacterial slime on the external surface.