Comments about some comments. Shorty stated - "bottom diffusers typically just aerate around the area the of the bubble column". Not completely true. Technical discussions about bottom aerators typically mention - turnover or turnover rate which means how often the entire water body will go through one complete circulation - bottom to top. The circulation pattern is sometimes affected by wind and waves. Sometimes the circulation does not involve the complete water column/volume but varying widths of the pond surface and basin. Testing verifies complete circulation. A complete circulation usually involves mixing and distribution of the available dissolved oxygen which can be increasing or decreasing depending on prevailing conditions such as size and number of bubbles, depth of the water column, amount of incident light, temperature, amount of plant biomass i.e. photosynthetic rate, etc.
Shorty mentioned "Notice the shaft is at a 45 degree angle creating current on the bottom." I ask, how deep is the bottom? I assume that all the downward force that the circulator is able to produce has a limit as to how deep it can penetrate? This limit is probably due to several physical factors, one of the main ones is probably horsepower. Additional ones are probably water mass (density) and inertia.
