See my 2nd link to Chuck's Planted tank page. In the middle of that page you will see a calculator that you can use to estimate CO2 if you know the pH and kH.
Right: For clarity, if we expect the 4dKH standard to turn green with the 30ppm CO2 standard/rule of thumb, the values above is for 45ppm CO2 with a 6dKH standard +/- 10ppm. Happen to know if the color thing is at least a linear relationship or does it go exponential?
The color thing will be considerably harder to "calibrate" as there so many variables in what goes into the human perception of color.
I don't think this is so important, but have never used a drop checker. The idea of using a Double Check Cal Aqua unit (or two standard drop checkers) from Orlando is simply to leverage a design with a reference sample (which is a great idea) to two different standards where you can use the maximum range for sample 1 and the minimum range for sample 2. Or even the "Too High" and "Too Low" colors. Its a better guess/estimate without the cost nor trouble of a more precise measurement.
Hoppy still posts on Barr's forum. I will refine this idea and post there for his critique, but when up for it I'll look through his posts too. He's so methodical he or Salt or someone probably has the formula posted in some thread. But if someone has it already, I'll make you the web calc for it
Or is this idea off base? If we agree the range of drop checkers is good enough for our purposes, I think we can also agree a tighter range from an inexpensive unit would be even better. Or is there another reason its a bad idea?
******** I am dumb: from Greenleaf's pics the Double Check unit from Cal Aqua clearly doesn't equalize gas in the second/reference sample. I just missed this until now.
