well, according to the simplified calcs, I have around 72ppm CO2. My fish seem perfectly healthy
One thing to consider is that the spread sheets are best case scenario meaning that all protons (H+) comes from carbonic acid. If you have any other source of protons such as tannic or humic acids,..like from driftwoods or peat...then the CO2 table OVERPREDICTS CO2 levels.
I really doubt that many people really have the CO2 levels they think they have (if just using the KH/PH table).