Re: pH swings, CO2

To: Aquatic-Plants at actwin_com
Subject: Re: pH swings, CO2
From: psears at emr_ca (Paul Sears)
Date: Fri, 29 Mar 1996 08:56:55 -0500 (EST)
In-Reply-To: <199603282039.PAA23165 at looney_actwin.com> from "Aquatic-Plants-Owner at ActWin_com" at Mar 28, 96 03:39:01 pm

> From: Michael Livingston <Mikel at netcraft-sw_com>
> Subject: Wild pH Swings

(snip)
> 
> After all that, what can I do to minimize these changes.  I have read =
> that kH (or is it alkalinity per recent flames :) ), pH and CO2 are tied =
> together.  

	They are.

> My water has a kH of 4 per the Tetra tests.  Will raising the =
> kH help stabalize the pH?  

	No.

> Can I use aquarium salt or baking soda to =
> bring the kH up?  Are there other better suggestions?
> 
> 
	If the aquarium salt is sodium chloride, no.  Sodium bicarbonate
will raise the carbonate hardness.

	The pH depends on the log of the CO2 concentration.  If you double
the CO2 concentration, the pH will drop by 0.3.  The size of the change
is independent of the carbonate hardness, unless that hardness is _very_ low,
i.e., less than about 1 kH.
	You can shift the range by changing the hardness, but its size will
remain the same.

The pH/kH/CO2 relationship can be calculated from:

	pH = 7.58  +  log(kH)  -  log(ppmCO2)

(The 7.58 is somewhat temperature dependent)


Paul Sears     Ottawa,  Canada