Re: Acids to lower pH (was: RE: Lime Deposits)

["David A. Youngker" <nestor10@mindspring.com>]

From: "Beaudry, Kyle : SEN"
Sent: Thursday, May 04, 2000 2:39 AM


> I have noticed that the majority of the commercially available pH
> down's are comprised of sulphuric acid.
> You said that you use muriatic, if I remember correctly from my
> First year Chemistry classes muriatic is Hydrochloric acid which
> when dissolved in water will dissassociate into Hydrogen and
> Chlorine ions. I spend a whack of cash buying water treatment
> product to remove chlorine from my tap water before doing my
> WC's. I assume you have been using the muriatic for some
> time, and you have not noticed any ill effects? Probably a simple
> explanation for this... it just got me to thinking and I was curious
> because one litre of muriatic is sure cheaper than the
> commercially prepared pH down out there. It was the thought
> that adding HCl to my tanks would cause problems so I refrained.
> Could anyone shed some light?
>
> Thanks

I haven't noticed a reply to this one yet, so...

Your chemistry's just a "hair" off. The resultant ion in the HCl breakdown
is indeed Cl-, but that's the *chloride* atom (hydrated to ionization,
actually). Dissolved chlorine *gas* (Cl2) is what you're removing with water
treatments.

The result of adding any "mineral" acid, whether hydrochloric, sulfuric or
whatever, is the release of the hydrogen ion and its corresponding mineral
base. We can all think of handy uses for the hydrogen, but the "base"
remains as a contributor to the Permanent measure of General Hardness. Those
who like to think in terms of conductivity can watch a corresponding rise on
their meters - they raise Total Dissolved Solids (a sort of loosely-defined
GH) with ionized particles. So there's a slight cautionary note (outside of
safe-handling concerns) in its general use to lower alkalinity and pH.

Since the buffer we're normally concerned with reducing is carbonate-based,
you should be aware of the "outcome". The carbonate-hydrogen reaction
eventually results in the outgassing of carbon dioxide - hence the removal
of carbonates and their replacement with mineral ions. An exchange of
temporary hardness for permanent hardness and a considerably more conductive
ion. And that's with a balanced reaction - if you overshoot the mark, you've
raised the conductivity considerably as well as dropped the pH. High mineral
content at low pH isn't a oft-occurring situation and can place an unnatural
type of stress on the fish. And the situation worsens as the initial value
for alkalinity or KH increases.

This is not to scare you off from using a well-known technique, just a
reminder to put some thought into its limitations - especially where high
starting values of KH and/or GH are concerned. But it is a right handy
technique for making small adjustments...

-Y-

David A. Youngker
nestor10@mindspring.com




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