03-26-2012, 12:29 AM
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OK, sorry to take the thread off topic, but a few things to add.
I've only heard the term 'temporary hardness' when referring to the ability to remove bicarbonate hardness via boiling, e.g. when heated, the bicarbonate changes to carbonate and carbon dioxide, the CO2 is driven out of solution and, assuming it was calcium bicarbonate to begin with, the carbonate and calcium form CaCO3, which can then precipitate out of the water, lowering both GH and KH, maybe 'temporary hardness' applies to bicarbonates independent of this process. This can't occur when Ca/Mg is present in the form of chlorides or sulfates, thus 'permanent' hardness (which is, as always, from Ca/Mg not from the chloride as it seemed to be suggested in the quote) rather than temporary. However, exchanging Ca/Mg carbonate with Ca/Mg chloride/sulfate, doesn't soften the water – the Ca/Mg is still there – though I guess it would help to reduce scale deposits.