I have a drop checker on the way from e-bay. I found an ADA one that I got for $26 brand new .If you use a drop checker per http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html you will have a much more accurate idea about how much CO2 you have in the tank. Measuring the pH and KH of the tank water doesn't give you an accurate measurement of CO2, and it generally gives a high reading.
This doesn't work either! I found when I did some testing on this method that 24 hours isn't really long enough for the pH of the water sitting there to stop rising. Another guy doing the same testing found it took more than 2 days, as I recall. And, it still isn't at all clear what the ppm of CO2 will be in the water after it sits that long. It could be 0.4 ppm, or it could be 4.0 ppm. In the first case the 1.0 pH change means only 4 ppm of CO2 in the tank water, but in the second case it means 40 ppm. And, a .5 difference in pH would mean about 70% of the amount of CO2 that a difference of 1.0 means. About a .3 difference in pH is what means 50% of the amount of CO2. (It is proportional to 10 to the power of the pH difference. 10 to the .5 power is about 7, 10 to the .3 power is about 5.)A more accurate way to check co2 would be to take a cup of water from your tank and measure the ph of the water. Then wait 24 hours and test the ph again. For every .5 difference of ph thats 15 ppm of co2. So for example if your ph was 7.0 on the first test and 6.0 on the second test you had 30 ppm co2 in your tank.