pH/KH/CO2 question

> From: tac2 at mtgpa_mt.lucent.com (t.a.castrovince)
> Date: Wed, 30 Oct 96 13:34:11 EST
> Tank info is: pH=7.6, GH=8, KH=5, temp=78, nitrates<10ppm, 25% water
> changes every other week, 12 assorted rainbow fish, one 20W Triton,
> gravel-only substrate, and one large piece of driftwood. Filtration is
> an AquaClear 300 power filter - no UGF.
> My question is, based on the pH/KH/CO2 table posted by George Booth, I 
> was expecting (and sort of hoping for) a drop in pH. But it never happened.
> Am I missing something? I am assuming that I have increased the amount of
> dissolved CO2 in the water

Your initial conditions indicate a CO2 of around 5 ppm, which is
consistent with a non-injected tank, so I trust your measurements. 
If your injector was able to increase the CO2 to 10 ppm, you should
see the pH drop to around 7.2.  Since it didn't, there are some 

1. Your reactor is not very efficient (although what you decribed
should work well),

2. The pH test kit does not have enough resolution to detect the
change that is occurring (although most seem to have a 0.4 pH
resolution, which should be good enough),

3. You have too much surface turbulence with the filter and CO2 is 
leaving as fast as it is being injected,

4. The "KH" you measured is not really carbonate hardness.  The table 
depends on the total alkalinity (being measured by most KH test
kits) to be predominately due to carbonate ions.  If the alkalinity is
due to other things (phosphate buffers, for example), the table won't
tell you much,
5. Your CO2 source is not very pure.

in Relatively Calm Colorado Compared to Yesterday's 100 MPH Breeze