Quote Originally Posted by Crusinjimbo
As I understand the air/water exchange principles, the actual gas exchange takes place at the surface where the air and water come in contact. The agitation of the water causes an incease in the volume of oxygen in the water. In other words, the bubbles rising through the water column add little to nothing to the exchange. It is at the surface. The greater the surface area the more exchange activity you will have. ?
You are forgetting the surface area of the bubbles themselves.

Thus, a long airstone creating a screen of many, many bubbles oxygenates the water more efficiently than sticking the end of a hose under water and releasing a single stream of bubbles.

This is of course an issue completely seperate from keeping the res well-mixed.