[imeridian]

Ca & Mg have nothing to do with determining CO2. It's not about TDS either. The problem with the chart is that there can be buffers present that the KH test cannot account for and acids other than CO2 that the pH test will be effected by.

 

[imeridian]

Doesn't KH measure ca and magnesium? Mine does... These charts have you measuring KH and ph and then determining the CO2 from them. Because there are other buffers (dissolved solids - ie. baking power is a dissolved solid, that changes ph, etc.) in the water it can skew your results. Maybe I'm missing something, but I only know to speak in laymen's terms.....

No, you've confused the GH (general hardness) test with that for carbonates (KH test). Baking soda increases KH, and subsequently pH, by adding bicarbonates to the water. It's the carbonate buffer to CO2 acid relationship that allows the CO2 chart to work. The General Hardness test is the one that measures Ca and Mg together. The GH test is completely useless for determining CO2 levels with the chart.

As I mentioned before it's the non-carbonate buffers and non-CO2 acids present in the water that skew the results making the chart inaccurate. It isn't TDS, it isn't Ca, nor Mg. A square is a rectangle, but a rectangle isn't necessarily a square.