I have a 260 gallon tank with a 135 gallon sump (approx 90 gallons operational). My kh hovers around 8 dKH. I don't know my gH at this point as I don't have a test kit for it at this time. Morning PH is 7.2x. I run the co2 from 2 hrs before the lights come on to 1 hour before the lights go out. My light schedule is from 13:00 - 20:00. My PH drops to around 6.2x through the co2 schedule. From what I've read I want to see a 1.0 drop in PH though the day. I currently get about .9 of a drop with my co2 set to 40psi and 25'ish bps. I thought that this was all good but then, in doing more reading, I've discovered KH and the PH/KH charts. With a KH of 8 and a PH of 6.2x, if I read the chart right, I'm looking at 120+ ppm of co2 in the water. My fish don't seem to be laboring at all so I'm wondering if I'm missing something.