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Re: more on CO2, hardness and pH

> From: ruddigar at home_com
> Subject: more on CO2, hardness and pH
> Hello
>   I was just checking out my favorite planted fish tank and noticed all
> was not good.  The first thing I did was test pH and found it very low
> (below 5).  So I added a teaspoon of sodium bicarbonate to raise it. 
> The pH crash must be attributed to the newly added DIY CO2, but my tap
> water is so hard that I'd figure it would never be a problem.
>   Water out of the tap:
> - - Calcium hardness 75 ppm
> - - Total hardness 119 ppm
> - - Alkalinity 66 ppm
> - - pH 8.1
>   I use Seachem's Acid Buffer to lower pH to 7 and usually drops to 6.6
> with CO2, but this morning it was dangerously low.

	You started off with water that would have been fine with CO2,
but by adding the "acid buffer" (which I will assume is the fully protonated
form of an amino acid (HOOC....NH3+ with a negative ion such as Cl-)),
you destroy some or all of the KH (bicarbonate). I suspect that you 
usually destroy just about all of it.

	If the pH ended up at 5, then I can definitely say that you
destroyed all the KH.  The buffering system is now:

	HOOC..NH3+   <->  H+  +  -OOC...NH3+

	This is fine for controlling pH in the range 4 - 6 or so, but
that isn't much help to you.

>  I literally lost a
> female flagfish (I can't find her anywhere) and the male died in the
> night.  Other fish are pretty stressed.  I hope I can save them.
>   Any suggestions as to what I can do to help/prevent the situation?

	Just use the tap water with CO2.  Using more than one buffering
system at once is asking for problems.

	Don't forget that the pH/KH/CO2 tables _always_ give correct answers,
but the KH is not measurable when there are other buffering systems there.
If your CO2 is fairly low, and the pH is about 7, then the KH is very low,
and it is low because the "acid buffer" destroyed most of it.  You don't
need to add much more "acid buffer" to take the pH to ranges you don't want
to see.

Paul Sears        Ottawa, Canada