One of the five keys to any healthy aquarium is aeration. In an aquarium with even moderate amounts of fish, aeration is essential for healthy fish. The aeration not only keeps the fish healthy, it keeps the beneficial bacterial populations healthy.
One way to get good aeration is by having the surface of the aquarium be water which has rough turbulent “choppy” appearance to it. This can be the discharge from a filter outlet or the flow from an in-aquarium pump (a “wavemaker” or a “powerhead”).
The other way to get excellent aeration is through the use of airstones. Contrary to popular mythology, airstones do an excellent job of aeration because of the many bubbles rising through the water, AS LONG AS THE AIR PUMP IS LARGE ENOUGH TO PUT OUT HUNDREDS OF BUBBLES PER SECOND.
If one has a well-stocked aquarium aeration becomes VERY important. If the aeration is shut down by something like a power outage, the results can be tragic. If one heavily stocks aquariums one needs to think about generators or battery-operated air pumps. I lost about several thousand dollars of large Mbuna when the power to my house went out once. I now have a generator.
It is also important to consider redundancy in aeration as critical in any heavily stocked aquarium. Let us say one has a heavily stocked tank with a bladed circulation pump aimed at the surface to provide the aeration. Bladed circulation pumps go out ALL the time. Now Murphy’s Law will apply here and the bladed pump will go out just after one has gone to bed. And in the morning one will wake up to a tank of dead fish. Think two circulation pumps or two air pumps in a heavily stocked aquarium.
There should be at least two devices providing aeration in any heavily stocked aquarium.
Aeration in More Depth
Here are the topics and chapters covered here:
9.1. Aeration in Depth
9.2. Aeration and Turbulence
9.3. Air Stones
9.4. Skimmers and Spray Bars
9.5. Aeration and Temperature
Source: Aquariumscience.org – David Bogert