Pond Boss Forums AERATION Systems questions Which way is best

Russ - Sorry for the delay; I'm currently very busy with other things. Bob has correctly summarized the basic concept of the air compressor & diffuser. I'll add a few more details. Bottom water in the pond is the first to lose its oxygen due to the high consumption of oxygen from decaying materials lying on the bottom. To a slower and lesser extent (not always), the deep water also loses oxygen from decaying matter falling through it as dead/dying stuff sinks, esp. important when a plankton bloom is decomposing or breaking down and sinking. An air diffuser producing small bubbles that are rising to the surface pulls water to the surface. The amount of air, size of the bubbles and size of the diffuser determines how much water is pulled to the surface.
At the surface where light penetrates, trillions of microalgae (phytoplankton) add oxygen to the water. In an algae/plankton bloom microalgae densities are often 3-12 million cells per ounce of water at least in the light penetration zone. This is why the water has a greenish tint. These cells range from 3um(0.003mm)to 1 millimeter long.
Some oxygen, but not much oxygen (compared to the total oxygen budget of the entire pond)is added to the water from the bubbling action. Mainly because, 1. oxygen is very insoluable in water (low solubility), 2. bubbles have a short contact time with the water and 3. air has only about 20% oxygen in it, not much available to dissolve into water. NOTE: Air diffusers are POOR emergency aerators; but good for keeping the pond water in overall good condition so you don't need emergency aeration.
Your main goal is to get large volumes of "bad" water out of the bottom to the surface where it is "cleaned up" & reoxygenated. Some decompositional gasses also diffuse out of the water at the surface.
Large volumes of water have to replace all the water that is moved out of the bottom to the surface and this water comes from surface to bottom currents that become established from the moving water spreading out away from the "surface boil". This is why it is better to have a stronger surface boil compared to a weaker boil from a small amount or volume of air from a smaller diffuser.
With the pond BOTTOM SEDIMENTS receiving oxygenated water millions of bottom animals can now live in and on the bottom sediments to quickly & and cleanly decompose/eat the organics and recycle them back into the basic chemical nutrients.
In "healthy" oxygenated pond/lake bottom sediments, there can be up to 80,000-180,000 aquatic worms (oligochaetes)per square yard plus thousands of individuals of several different types of insect larvae. This does not include all the protozoans, rotifers, snails, fingernail clams and bottom zooplankton that can also inhabit the oxygenated sediments. They all are responsible for processing the dead organic materials that have settled to the bottom. NO, catfish do not eat this stuff; small critters & bacteria do. Without oxygenated water on top of the deep water sediments none of these tiny animals can live on the pond bottom. I hope this helps you and others understand the benefits of moving your pond bottom water to the surface with an air compressor and diffuser. B.Cody-Pond Doctor