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**To**:**Aquatic-Plants at actwin_com****Subject**:**Re: Stoichiometry Anyone?****From**:**"Roger S. Miller" <rgrmill at rt66_com>**- Date: Sat, 14 Jul 2001 10:10:31 -0600
- References: <200107140748.f6E7m5E28611 at actwin_com>

Todd H. wrote: > If my understanding of the definition of KH is correct, then this > formula seems to have an incorrect conversion of KH to moles HCO3-. > Is it correct that: > > 1 GH = 1 KH = 10 mg/L CaO = .3566 meq/L = .3566 mmoles/L HCO3-? > > For the result to indicate dissolved CO2 in mg/L, shouldn't the > constant > be: > > .3566 * 44.01 mg/mmole = 15.694 rather than 12.839? GH is defined in terms of CaO, but I think KH is actually defined in terms of CaCO3, with 1 KH ~ 17.86 ppm CaCO3. However, the way you did the calculations, that makes no difference. This is actually a fairly long-standing controversy. I summarized some of what I could find about the different constants used in the formulas and who used what in the letter at http://www.actwin.com/fish/aquatic-plants/month.9707/msg00222.html Briefly, the lower constant has been in use for a long time, but some of us use the higher constant. We have additional uncertainty in the value of pK1 and in our pH and alkalinity measurements, so the 22% difference in the constants may not be as important as it looks. Roger Miller

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