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Re: Another question about water reconstitution

> From: "David A. Youngker" <nestor10 at mindspring_com>
> He's looking to reconstitute pure water. The calcium carbonate will add both
> calcium and buffering to this.
> > You can get food grade calcium hydroxide in the canning
> > and pickling supplies at your local grocery store.  It is called
> > "pickling lime".  I *think* it is more soluble than calcium
> > carbonate, but you'd have to be more careful about its affect
> > on the pH.
> Ca(OH)2 is indeed far more soluble than CaCO3 - about a hundred-fold as much
> at aquarium temperatures. The shift in pH will be sudden and dramatic rather
> than (relatively) gradual.
> With each molecule of Ca(OH)2 that ionizes in solution, _two_ hydroxide ions
> are released. Where the carbonate ions from a comparable amount of CaCO3
> will draw out hydrogen ions in a conversion to bicarbonates, its effect is
> "limited" compared to the addition of a considerably _larger_ body of
> hydroxides. The balance of H+ to OH- is shifted directly (in addition to
> those H+ ions consumed in neutralization), and pH will skyrocket.
> To say that you *think* it is more soluble implies that you possibly haven't
> worked with it directly - otherwise you'd be *sure* of both its solubility
> and its effects on pH...

You are right, I have no direct experience with using food grade
slaked lime in an aquarium and I didn't bother to look up its
solubility.  I mentioned it as a readily available and cheap form of
calcium ions without any significant impurities.  It could probably
drive the pH of distilled or deionized water all the way to 14 because
it has no buffering capacity, but it would still be useful if you were
buffering the pH with other acids and salts in your mix.  I did warn
that it would affect the pH...

Best regards,