The whole point of using a drop checker is to make the CO2 chart work. It doesn't work when used with typical aquarium water, because there are too many things in the water that affect the pH, other than just carbonates and CO2. With a drop checker you are measuring the pH of a tiny bit of water that contains nothing affecting pH except carbonates (bicarbonates) and the CO2 that equalizes between the drop checker water and the tank water. The La Motte CO2 test is also a pH/KH test, so is also inaccurate. But, you can buy a CO2 probe and meter that will very accurately measure the CO2 concentration in the tank water, and do it very fast. All you need is a couple thousand dollars to spare.