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KH/pH/CO2 Chart

Kelly wrote about her new CO2 setup:  >>> I'm not sure if I understand
the pH chart correctly.  Let's say that your dKH, without CO2, is 4.  If
you want 19 ppm CO2, you want your pH to be 6.8.  Does that mean that
your KH before CO2 is 4, and you add enough CO2 to drive your pH down to
6.8, or does it mean that with CO2 injected water and a pH of 6.8, that
your KH should be 4?>>>
The first statement is correct.  If you start with a dKH of 4 and add
enough CO2 to drive down the pH to 6.8 you will have 19 ppm CO2.
Injecting CO2 will not change your dKH.  So you start with a KH that
will give you a pH in an acceptable range at the CO2 ppm you target.  I
think your target (19 ppm CO2 and dKH 4) is just about ideal.  I try for
5 dKH, 23 ppm CO2 at a pH of 6.8 in my tanks.
Let's say your water has a dKH of 2.  If you add enough CO2 to reach 19
ppm, your pH will be around 6.5.  Or if you start with a dKH of 6 and
add 19 ppm CO2 your pH will be about 7.1.  Both CO2 and dKH affect pH.

Kelly also wrote:  >>>Last night I got up a few times to check the pH
and the fish.  I didn't want it to get too low, and I didn't want to
shut the CO2 off.  It stabilized at 7.16 or so, and the fish never
seemed to be stressed.  This morning when the lights came on I turned it
up just a hair.  I'm using the Eheim reactor, and although it produces
tiny bubbles, I'd like to do something to completely make sure every bit
of CO2 is dissolved.  I think most all of the bubbles reach the surface
sooner or later.>>>
With a dKH of 4 and the pH at 7.16 your CO2 was between 6-8 ppm-not
enough for the pearling you want.  You need to  crank up the CO2 a bit.
I've done two things to maximize the amount of CO2 dissolved in the
water column.  Put the reactor as low in your tank as possible to give
the bubbles as much time to dissolve as possible.  I also aimed my
canister filter water return bar toward the CO2 reactor so that the
return water would push the bubbles back down toward the gravel.  I
wouldn't worry about losing a bit of CO2 though.

Regards, Steve Dixon -- San Francisco