Originally Posted by Bunsen Honeydew
I don't understand why Barr would use such a simplistic methodology, especially since he was putting the outputs into a chart and there are several well established methodologies in the literature already.
No idea which methodologies you are referring, to my knowledge there is no 'easy' way without expensive equipment or tests to accurately measure CO2 levels in an aqaurium.
Tom Barr publshed something simple for hobbyists to use and reference, but the limitations are only understood and explained properly by some.
Even the approximation that 1ph drop is 30ppm may not be accurate depending upon what other unknowns are in the water and atmopsheric pressure and temperature. For all we know many people have 2ppm dissolved in their water not 3 and only 20ppm CO2 instead of 30 and yet their plants are doing fine.
I am setting up a new scape this week, my spiderwood drops the pH in the tank by 0.3. If I used the Barr chart, my kH is the same, the CO2 injection is the same, however my pH is different. Now according to the chart I'm supposed to have 94.6ppm CO2 in my tank, that is lethal for fish and of course completely overstated, I have the same amount of CO2 injected as I did before I put in the spiderwood.
All he needed to do was cut and paste different formulas into his excel file.
Not sure what you mean by that, paste the formulas here you would use.
There are a few things from your explanation that I either do not agree with or understand. The first is why you are putting so much weight on missing initial pH and GH.
I never said anything about gH anywhere(never wrote that term) it is irrelevant, the kH is what is important.
If you agree the chart is rubbish, and you measure your tank water after it has been degassed to capture pH, then you add CO2 to reach a target pH drop of 1 which could approximate 30ppm than we are finally on the same page.
Measuring kH is also not necessary, the approximation is reasonable as long as your kH is between 1 and 10.
Could you expand on the logic of why the GH is important?
It isn't for calculating CO2. I think that confusion is that my original post referred to Carbonate Hardness (kH) or Hardness of Carbonates which if you just read hardness you might think I was referring to General Hardness(gH).