I agree with most of what you say, but not about adding O2 at the surface. Removal of Co2 is not as important as fish do not respond to it in the same way as mamals. Lots of studies show that the amount of O2 absorbed by the water is a function of pressure. The higher the pressure, the more oxygen is absorbed. This means that a stone deep down is more effective than one near the surface.

My mentor designed and built recirculating systems powered by air lift pumps for intensive tilapia growth. He dug tubes 50' down for the air lift system and injected the air at the bottom. The water as it came out of the lift tubes was oxygen saturated and these tubes provide all the motive power for the raceway and biofilters.