The pH KH chart is not very accurate, it can be thrown off by huge amounts by having other things in the water. The easiest, cheapest way to monitor Co2 is with your drop checker. It cant be fooled by other dissolved components in the water so its accurate as to whats going on, and you wont be aware of your exact Co2 level but you will be aware of the general area your level is in.I have a 10 gallon tank that is medium planted with a 36W Kit from AHsupply. I am using DIY Co2 and one of those knock off glass co2 diffusers from ebay. I also dose pps pro. Using a "Tetra-test" kit i measured pH = 6.5 and KH = 8 .. so accordingto the chart that came with the kit i currently have 70 ppm Co2?? That doesn't seem right since my bubble counter is at about 1 bps.
I've also taken out all my fish and put them in another tank for now and turned my biowheel off. Going to try to accelerate the growth of some HC i bought to make a lawn.
In other words ditch the chart and monitor with the drop checker, make sure the correct color is in the bubble and you are good!