Re: [AGA Member] CO2 concentration in Hard water

[Erik Olson <erik@thekrib.com>]

On Mon, 10 Nov 2003, Amit Brucker wrote:

> So is using more CO2 to
> > > hold that pH range if the KH is high is correct ???
> Also as the 'I think what Red Sea is saying is that *IF* you limit
> > > > yourself to pH values' as well ???

> Hope I am starting to understand something here... what would be the case
> where the KH is low ????

If you start from the concept that KH and CO2 are independent of each
other, but help determine pH of the water, you can get everywhere else
from there, including Red Sea's somewhat misleading statements.

Lower KH  -> lower pH
Higher KH -> higher pH 
Lower CO2 -> higher pH
Higher CO2-> lower pH

But as Roger noted, increasing KH doesn't really induce an "ability to
absorb more CO2", just means that if you're shooting for a particular
desired pH, it will take more CO2 to do so than at a lower KH.  But you
would have to physically crank up the injection rate to keep the same pH.

Now, if the KH is ridiculously low (like < 1 degree sometimes in our water
here in Seattle), then there is so little buffering capacity that the pH
tends to swing kinda wildly with the amount of CO2 (as well as other acids
and bases from the fish waste).  But of course, at that KH, the water is
already below 7.0 when it comes out of the tap, not particularly good for 
plants.  I *have* to add calcium and mag carbonate just to keep things 
stable.

  - Erik

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