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Re: CO2

> > PO4 - 0 to 0.5 ppm
> Phosphates in your water will be seen by your "KH" test kit as additional KH.
> It's not really KH, but additional alkalinity. Remember, KH test kits are really
> measuring total alkalinity with the assumption that carbonates are the only
> contributor. If you have phosphates in the tank, this assumption is false. Be
> careful here.

Are there any KH kits that actually measure carbonates?

George, Do you have any impression of how much phosphate it takes to
throw off the KH measurements?   

> The CO2/KH/pH tables assume that the only alkalinity is from KH. If you have
> phosphates, the tables will NOT give you correct results.

> > With the following tank parameters, what can I expect regarding pH and
> > hardness changes. (I'll be turning the system off at lights out)
> >
> > pH - 7.0
> > dkH - 4.0

> No, with a KH of 4 and 15 ppm of CO2, you will get ph = 6.9.

You say that 15ppm of CO2 will be a pH of 6.9, but his pH
is already at 7.0 before CO2 injection.  So, the chart would suggest
that with a KH of 4, and a pH of 7, he's already got 12ppm before
adding any CO2!  But we know that's not true.    

It's probably the phosphates throwing off the numbers.    Which
makes the values on the chart incorrect.

BUT! With the phosphates influencing the buffering, does the 
relationship itself hold?  Will increasing the CO2 10 times still
drop the pH by one full point?  Or is that relationship broken by
the phosphates as well?

If that relationship still works, then:

If we assume that his non-injected water has ABOUT 2-3ppm C02, then with
a pH of 7, his "real" KH would be about 1 degree, so if he targeted a
pH of 6.3-6.4, that would put the CO2 in the right ballpark, about

Is this completely off?    If so, it might be a way to still let people
use the chart when they have high phosphates

Chuck Gadd
Director of Software Development, Cyber FX Communications
e-mail:cgadd at cfxc_com  http://www.cfxc.com