for the week of 7/8/99

Fish extract dissolved oxygen from the water and exhale carbon dioxide, creating a shortage of the former and an excess of the latter. Aeration is the process of returning these two dissolved gases to their normal proportions.

Circulation. An important part of aeration is to move water from all parts of the aquarium so that it comes into contact with the “air/water interface.” which is a pretty fancy way of saying “water surface.” It is at this point that gases are exchanged: oxygen in, carbon dioxide out of the water.

Surface agitation. In order to allow easy gas exchange, the surface tension of the water and any floating oily films must be dispersed.

Airstones. The air pump and airstone combination is still among the most reliable aeration systems available. While the bubbles themselves do not contribute as much oxygen as once believed, the water flow patterns they produce circulate efficiently from bottom to top, and the bursting bubbles agitate nicely as well. Better yet, even if the airstone is in a filtration device, it continues to aerate even if the filter media is plugged.

Power heads. These motorized water pumps can also be effective aerators – especially if they utilize an air injection (“Venturi”) device to better agitate the surface. They can move quite a bit of water, but generally require more frequent attention to keep pre-filter media and venturi intake from clogging.

Power and canister filters. These also aerate quite well, but only when they are very clean. As their filter media get dirty, water flow usually slows greatly, reducing both the circulation and surface agitation provided. It is best not to rely on these as the sole source of aeration.

Plants. While it’s true that plants produce oxygen and use carbon dioxide, this only occurs during the hours that the light is on. During the darkness, they are yet another oxygen consumer. Obviously, this makes them practical as aerators only in tanks with small fish loads.

“Tip of the week” appeared regularly in 1999 and 2000.