Dazzer
As far as i can see your assumptions are correct. If you are concerned about your fish and for whatever reason you are not comfortable with CO2 levels of 30ppm in your water an easy solution is to set up a low tec non-CO2 tank.
A high tec tank that is pearling with lights on has supersaturated O2. You could not pumps this much O2 in a tank with air stones alone. If fish were experiencing shortness of breath in such a case in the abscence of surface agitation then you could correctly assume it is CO2 poisoning (hypercapnia). I think surface agitation does facilitate in driving off excess CO2 that is not utilised by photosynthesis and at the same time introduces O2 into water.
You would have to look at a physiology text to see what the affinity of CO2/O2 to the Hb molecule is. I cannot remember the biochemistry but there is a definite relationship.
LAKA