Well I don’t have the formula in front of me, but isn’t hardness 7(Ca) + 3.5(Mg)?
I’m sorry I don’t really follow the rest... the hardness as CaCO3 is already correlated to alkalinity as CaCO3. That’s why they use the correlation.
The thing about hardness and alkalinity staying the same while calcium and magnesium fluctuate can’t be absolutely true as those minerals are the primary constituents of the hardness component.
So what I’m getting out of all this is that you’re trying to derive your bicarbonate value, but it’s not stated on your published water report (which is kinda unusual), and you haven’t had it lab tested. Is that correct?
If that’s the case; you can’t derive the alkalinity AFAIK. It must be measured. Hardness can be derived from Ca and MG. You can measure alkalinity at home pretty cheaply, with a total alkalinity kit. Which is usually bromocresol green/ methyl red, titrated with sulfuric n/50 (that’s from memory someone correct me if I’m wrong). I think it’s 25ml water couple drops of the indicator titrate from green to red. ML’s used multiplied by 20 will give you your total alkalinity as CaCO3. You could also send it out to ward labs, or call your water supplier, they’ll have the data. These are just snapshots in time though, measuring the water coming out of your tap on the day you use it is far more accurate. That goes for hardness as well. It’s easier to measure it, then go by averages. If this for your spreadsheet I’d suggest putting in an input device for the titrations for those who want to measure on the day. There really is no substitute for measuring those variables, if you want your pH model to be accurate, as fluctuations in those parameter assumptions will change the residual alkalinity. The model will then generate an incorrect output.
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