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> Date: Tue, 2 Jul 2002 22:44:32 -0500 
> From: Michael Batts <Michael at whatisdat_com>
> Subject: Co2-KH-PH-AARRGGHH!!!
> Hmmmm, thought I had this stuff licked.  Guess not...  I thought that Co2
> lowered PH AND KH.

	I never cease to be amazed at the misunderstanding of what is
actually something quite simple.  CO2 lowers pH, but does not affect KH
(bicarbonate concentration).  The CO2 concentration and KH _together_ set the
pH.  Increasing KH raises the pH, increasing the CO2 concentration lowers
the pH.  There has been quite a bit of discussion of formulae or tables
that desribe the mathematical relationship between them.

	Where is the continuing misinformation coming from?

>  My tap PH is 7.6 and Kh is 15.  I started with 100 drops
> per minute of Co2.  This dropped the PH to around 7 and the KH to around 9.

	The KH drop was caused by something else.  It doesn't sound as
if the CO2 concentration increased by very much - I make it a factor of
2.4.  That is if the KH numbers are good.

> Good, but not good enough. Time to drop some more.  Soooooo, I increased the
> Co2 to 120 DPM.  Viola! the PH started to drop and settled at 6.8, SPOT ON!!
> (so I thought)...  Now the KH has raised to 11!!

	I doubt that the KH changed at all.  I suspect the measurements.

>  Run this through a ANY Co2
> calculator and it is still bad!!!  I thought the KH dropped WITH PH???

	No, the pH drops if the KH is lowered - you have it backwards.
You can destroy KH with a strong acid (e.g., hydrochloric).  This will
also increase the concentration of CO2 (temporarily), which will cause an
immediate drop in pH, followed by a slow swing back, though not quite
to where you started.  Cutting the KH by a factor of 2 lowers the pH by
log(2), which is 0.3.

	HCO3-  +  H+  ->  CO2 (leaves)  +  H20

>  Why
> did this happen?  Should I try to drop the KH manually?

	What do you mean?

>  I should like to
> see it at about 5.  What method is best?

	Dilute it with RO water - that's what I do.

Paul Sears        Ottawa, Canada