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Re: CO2 tables .....
> From: "S. Hieber" <shieber at yahoo_com>
> Subject: Re: CO2 tables - or how to save money..
> Paul Sears gave a new formula (vis-a-vis the two I had noted) and
> described a basis for using diferetn values at different temps:
> > By my reckoning, the formula should be:
> > CO2 (in ppm) = 15.7*KH*10^(pKa(CO2/HCO3- system) - pH)
> > T (C) pKa
> > 0 6.58
> > 5 6.52
> > 10 6.47
> > 15 6.42
> > 20 6.38
> > 25 6.35
> > 30 6.33
> > Pick your pKa.
> Thanks, Paul.
> Indeed. It's duly noted that test kit readings will give variances far
> beyond the differences in formulas.
> Still, it's nice to have in a CO2/KH/pH table, either an accurate
> formula (even if the accuracy is only for a cited temperature) *or*
> numbers rounded to the nearest 5 or 10 units. :-) At least then,
> there's a basis for reconciling the different formula or versions of
> the chart. Things are confusing enough without the math seeming to not
> work out. :-)
Agreed. One should get things right. I do think, though, that
people are worrying far too much about the precise concentrations of
things in their tanks when it doesn't really matter that much, and
our test kits aren't very good.
> Picking a last shread of mote from the nit, it looks like the
> "15.664*KH*10^(6.37-pH)" formula or "15.7*KH*10^(6.37-pH)" is a good
> for about 70 degrees F. A more likely *tropical* tank temp is about
> 78-80 degrees F, which would put the formula thus:
> 15.664*KH*10^(6.34-pH). Or should we just call it 16*KH*10(6.34-pH)?
To add to the motes and nits, if you want the factor at the
start to lots of decimal places, I make it 15.696 to three places. :)
That is using accurate atomic weights.
Now to start reading my KH test kit to four significant figures....
16*KH*10(6.34-pH) looks good to me for about 27 C.
Paul Sears Ottawa, Canada