With peat in the water you'll get an accurate kh number, it's the ph that gets scewed to the acidic side which throws off the kh/ph/co2 relationship. Even if the peat removes some kh ,the kh readings will reflect actual kh hardness. The problem is the humic and tannic acids that peat releases into the water column that acidify the water. If there is anything in the water column other than carbonates (ie:phosphate,acids or other non carbonate buffers) buffering the water, you're chart is rendered useless because of the effect on ph readings.
FILSTAR Pimp #2
75 gal heavily planted,50/50 Black beauty,Eco-complete substrate, Pressurised CO2 with solenoid, ph controller, AB Reactor 1000, 330 watts 9325K GE PC lighting,Ehiem Liquidoser, 2-Filstar xp3 canisters.