CO2 and KH


ha ha ha. I asked another chemist and got opposite answer. He said, the
same ammount of CO2 will be used to establish a certain concentration of
dissolved CO2 at different HCO3- concentrations. 
Only the pH will be different. It's perfectly logic if you just look at 
the Henderson Hasselbalch equation if you have an equilibrium, but it really 
doesn't explain very well the CO2 _consumption_ needed to achieve that 
equilibrium. He explained it with the order of maginitude (100,000) higher 
HCO3- concentration than H+ concentration. Any effect of saving CO2 would 
be very small. I think an experiment is needed. I will try to see what 
the CO2 consumption is in my aquarium if I lower the KH from 180 ppm to 
90 ppm and keep the CO2 constant at 18 ppm. I believe a rough estimate of 
CO2 use can be made by observing the water level in my Dupla type $ 
reactor. I have observed that it's fairly constant for a certain pH (or 
CO2 level) in the water. What do you think? A significant saving in CO2 
should be reflected by a rise in water level.