Back about 4-5 years ago when I first began to work on how to use an ADA Drop Checker as a CO2 indicator I quickly decided that we should use a green color to mean "good", which meant a pH of the drop checker fluid of about 6.6. That was to let us see if we were too high or too low. Using 30 ppm of CO2 as "good" CO2, that meant the fluid had to have a KH of about 4 dKH. Then I never once reconsidered that aspect of using a drop checker.
A week or so ago I started using DIY CO2, and wanted a drop checker to verify that it was working well. For this I didn't need to see anything except that I exceeded some minimum amount of CO2 in the water, and it finally occurred to me that yellow is a much better color with that reagent. Yellow is easier to see, and the gap between yellow-green and yellow is smaller in pH. This thread shows what I did: https://www.plantedtank.net/forums/fe...r-diy-co2.html
To my surprise I have more than 20 ppm of CO2, but that also means I could have too much CO2, as unlikely as that seems. So, rethinking the problem, I decided that using two DC's or a two chamber DC would work best, with one becoming yellow when 20 ppm is reached, and the other when the maximum allowable CO2 was reached. Since we still don't have an absolute maximum allowable CO2 number to use, I decided to use 60 ppm as the absolute maximum - exceed that and dead fish would quickly follow. If yellow indicates 60 ppm, the fluid in the DC should be 2 dKH. With 2 dKH fluid 30 ppm would be just slightly green-yellow.
To test this I made a two chamber DC, using the design that pdavis41 showed in this thread: https://www.plantedtank.net/forums/di...p-checker.html
which is a very flexible design allowing a very small DC to be made, which should also improve the reaction time. Here is what I made:
And, this is the chart for what the colors mean:
I loaded the two chambers with .75 dKH and 2 dKH fluid premixed with API pH reagent and installed in my tank. After only 30 minutes the two chambers clearly showed their final colors, and after an hour the colors stayed the same. Here is how it looks:
This tells me I have more than 20 ppm of CO2 and safely less than 60 ppm. I'm really pleased with this, and may save my pennies and buy a couple of the latest DCs from GLA to replace my crude little one. I'm convinced this offers enough advantages to justify using 2 DCs and making two standard KH fluids to use in them:
Much easier to read,
Good for DIY as well as pressurized CO2