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Re: Aquatic Plants Digest V2 #1086
> what is a good chemical source of calcium that won't increase carbonate
> hardness? CaCl? Will it affect pH?
> do humic acids interfere with measurements of carbonate hardness? would
> it cause a positive or negative error in measurement?
A four-line post? Are you feeling well, Steve?
CaCl2 should work in dilute solution. Calcium sulfate also comes to mind.
Calcium sulfate isn't real soluble - but its more soluble that calcium
carbonate. I think I've seen it for sale as a horticultural supply.
Plaster of paris is a partially hydrated form of calcium sulfate.
Many acids (mostly organic and at least some that could be soil-derived)
have the potential to interfere with the alkalinity test; all that is
required is that the acid have a pKa in (or really even near) your water
pH and a pH of 4 or 4.5 where the alkalinity titration ends. They make the
alkalinity appear to be higher than it actually is.
As a practical matter I suspect that the concentration of those acids
would have to be unusually high (or your alkalinity would have to be very
low) before the interference became significant.
The common chelating agent EDTA is an organic acid that could potentially
interfere with the alkalinity test.