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**To**:**aquatic-plants at actwin_com****Subject**:**Re: Calculate CO2****From**:**Roger Miller <rgrmill at rt66_com>**- Date: Mon, 1 Jul 2002 18:36:10 -0600

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

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