Good basic information so far. Tests by employees at OvertonFisheries verifies that bottom diffusers do not add "a lot" of DO to the overall pond oxygen budget.
When reading about efficiency of diffusers one has to be aware that efficiency of a diffuser can apply in at least two areas. Efficiency of the transfer of dissolved oxygen to water AND or efficiency of the amount or volume of water that a bottom aerator can move per hour based on a given cfm of air.
The main benefit of bottom aerators is they can "fairly cheaply" and efficiently move the water with poor quality out of the bottom zone where it developed this poor quality. Bottom aeration gets the deeper "bad" water to the illuminated surface zone where it naturally gets "refreshed" and oxygenated by several means including but not only limited to oxygenation by algae and higher plants and diffusion of several gases by mixing with the atmospheric air.
