After some 2/3 of my fish died in a recent CO2 tragedy I followed a member's advice and finally obtained and set up my first drop checker to monitor my CO2 injection. I believe my use of a high pressure Archaea diffuser with my Azoo CO2 regulator did not show how much CO2 was really being injected into my tank. I have since switched back to a lime wood aerator until my glass diffuser arrives. I purchased a good drop checker from Green Leaf Aquariums - this model has a reference bowl under the test bowl so that all you have to do is match the reference bowl color and the correct amount of CO2 is being injected.
Since this is my first drop checker I have some questions: I have my test bowl almost at the reference bowl color it is perhaps one or two shades of green lighter than the reference bowl so I assume that I have to reduce the amount of CO2 slightly with the needle valve until the colors are identical? How long does it take before I should check the colors - 2-3 hours or longer? The instructions say that a blue color requires more CO2 and a yellow color means a reduction of CO2 is needed as the reference green color is best. Also what do I do with the drop checker during my weekly water change? Does it stay attached? Do I have to refill it?

Thanks for your input and advice.

Those are cool DCs. Did you get any 4dkh solution with it?

Most guys on planted sites try to get the shade a pale green. So if you get there, you should be okay. I would watch it and make sure it doesn't go any lighter though.