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Re: Keeping pH down

> From: MarkyTkd at aol_com
> Subject: Keeping pH Down (Muratic Acid)
> How do I keep my pH down? Previously I had problems with lowering it. Now I
> can't keep it down. I used a little Muratic Acid (31.4% Hydrochloric Acid) to
> lower my pH. It would drop all the way to 6.4 and my fish would gain a bright
> red color. My fish (blood parrots) need a pH of 7 or lower in order to have
> red color. If the pH is 7 or higher my fish turn a pale color. (It's kind of
> like a pH test =P) After about 8 hours the pH shoots right back up to 7.4. 

	When you add a strong acid, you destroy bicarbonate ion and generate
CO2.  The reaction:
			H+  +  HCO3-  <->  "H2CO3"
	gets pushed to the right.  The CO2 leaves over the next few hours,
and the pH rises again.  To get a permanent effect, you must add enough
hydrochloric (or other strong) acid to destroy most of the bicarbonate
(KH) in the water.  To cut the pH by 1.0, you must reduce the KH by a factor
of 10 (10^pH reduction).  _Don't_ try to do this in one step, because
if you destroy _all_ the KH, the pH will crash.  Keep adding small amounts
of hydrochloric acid (muriatic for those still in the 18th century),
and you will eventually get there.

	It is a lot easier just to dilute your hard water with RO water.

It will be difficult to keep a stable pH of much below 7 without using
CO2 in the tank.  The alternative is to have a very low KH, which could
easily be destroyed by acid addition, e.g., the nitric acid from
oxidation of ammonia excreted by the fish.

Paul Sears        Ottawa, Canada