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Re: Another question about water reconstitution

> Date: Sun, 20 Aug 2000 14:17:32 -0500
> From: zxcvbob
> On Thu, 17 Aug 2000, Bailin Shaw wrote:
> >
> > Anyways, to my question.  I went to the grocery store
> > yesterday and was looking at the calcium tablets.
> > There are so many types and the ingredients vary
> > from one brand to another.  What are some of the
> > extra ingredients that are in the tablets that you use
> > beside from calcium carbonate?  I don't want to add
> > something that is going to be harmful to my fish.
> I'm not sure what you are going after with the calcium
> carbonate, I've been out of town for a while and have
> just read a week's worth of APDs in one sitting.

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...


David A. Youngker
nestor10 at mindspring_com