Ah this is at the very heart of what I am asking, but with my tired mind and poor explanation I failed to reduce it down to this cogent sentence I have quoted above.

The assumptions I am working under is that it is irrelevant to the fish how much o2 is in the water (providing the surface area/stocking rule has been applied there will be sufficient o2 in the water for the fish) as increasing o2 makes no difference to the fish, how it deals with co2, as the problem with suffocation of the fish, is not one of low o2, but of high co2 which prevents the fish removing co2 in its body via osmosis into the surrounding water.

Thats essentially what I am asking, because if that assumption is correct, then seeing as increasing surface agitation does nothing for the fish and it also helps to drive off the co2, then isn't it more efficient to simply not agitate the surface of the water thus attaining the desirable co2 levels while at the same time using less co2?

As for whether my own set up is either too high in co2 and the problems I am having etc. I am having no problems, and haven't with this and fish health since the first week after using pressurised co2 a good year ago now.

However, these are still questions I think would be interesting to know the answer to and to have a discussion about as I want to know whether my assumptions hold true or not, if they do, great, lets move forward and explore this, if my assumptions are incorrect, great, I can move forward and put that out of my mind.