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# Re: Calculate CO2

```Chuck H wrote:

> Scott H wrote in response to my posting of a formula for calculating CO2:
>>I believe Roger Miller has an alternative formula:
>>
>>    CO2 = 12.839 *KH * 10^(6.37-pH)
>>
>>The resulting values are nearly the same as the "3 * KH * 10^(7-pH).
>>
>>Roger, if you're listening, care to comment (or correct?)

>Perhaps I can save Roger a few keystrokes, Scott. :) The following URL leads
>to a post by George Booth which details the
>reasoning behind the equation he and Roger developed which Scott mentions
>above.

>http://fins.actwin.com/aquatic-plants/month.9707/msg00211.html

>This next URL jumps to a post in which Carlos Munoz shows the mathematical
>link between Roger and George's equation and the one I posted for Greger.

>http://fins.actwin.com/aquatic-plants/month.9707/msg00212.html

Those links are fine.

When we start throwing formulae around we should keep in mind that there is a
problem here.  Some people (including myself) disagree with the unit
conversions that lead to the value of 12.839 in the first formula above.  The
value of 3 in the second formula is based on the same unit conversion.
There's fairly extensive discussion of the difference in the archives, but it
really isn't easy to find.  For the alternate versions replace the first of
these formulae with

CO2 = 15.664*KH*10^(6.37-pH)

and the second with

CO2 = 3.6*KH*10^(7-pH)

The KH-pH-CO2 charts and tables have never been changed to reflect this
difference because (1) when you consider all the other possible problems with
the method the change would be a fairly insignificant improvement (2) because
George has never agreed and (3) because noone has bothered to do the work to
recalculate everything.

Roger Miller
```