If you mean ask Dr. Barr, a.k.a., plantbrain - he isn't a big proponent of drop checkers. If you use a 4dKH solution, the color changes to a blue-green at around 19ppm, then to green-green around 30 ppm, and to a green-yellow when CO2 levels have reached 47 ppm. IME, not a bad guide really, if you can live with the delayed response. I've used them but got tired of fishing them off the bottom of the tank after their suction cup lets go of the glass. Now, I find it's easier to check my pH and keep an eye on the fish.
IMO, this is basically what people who use a regulator with a pH controller do, set the controller to shut down CO2 when the pH drops to set point, using the pH/KH/CO2 table to determine the pH.
I'm saying, to dial it in closer, check the pH of a water sample after it gases off CO2 for 24 hours and compare it to the drop in pH, in the tank, later in the day. If it is less then a 1-1.3 degree drop and the pH controller shut off the CO2, make an adjustment to tune it in further but carefully adjust from there. I would be interested in hearing from anyone, particularly if they have experience using a pH controller, if they have tried testing the drop in there pH relative to ambient CO2.
Keeping CO2 enriched tanks is a daunting task. The equipment alone is scary and any test for CO2 levels is fraught with possible errors. That's why I had a hard time using anything other then yeast. CO2 regulators and their potential, is intimidating.
Keeping CO2 levels around 20 ppm, providing mid-levels of light and growing easy plants is not as fearsome and has a lot going for it. Some people might do nothing to measure CO2 other then watch their plants/fish and they have successful tanks under a wide range of conditions and lighting levels. They probably have a lot of experience under their belt. Others don't measure CO2 and kill fish. Others think they are deficient in Ca, or K, claim their Mg levels are too high or declare phosphate levels are out of balance - when CO2 and light are hardly given the attention they deserve. The more we know, the less frightening and ambiguous CO2 enriched tanks become, the more we can help each other. That's all.
fredyk wrote:Pertaining to the joke, is the answer like the following: second prize 2 weeks in philadelphia; 1st prize 1 week in philadelphia? (disclaimer: philly suburbs=my hometown)
If you know the answer, you get a red neck like mine.