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kH/pH/CO2 ???

Hi all.  Many thanks for the help with my green hair algae, especially to
Ken Whelan and Tom Barr.  It's all but gone thanks to (I think) increased
PMDD and pressurized CO2.

I have made an odd observation.  I've been examining the kH/pH/CO2 chart
found on the SFBAAPS and other web sites, and I decided to check out where
my tank falls on there.  I have a Red Sea "Plant Lab" CO2 test kit, a Hagen
alkalinity test kit, and a Tetra pH test kit.  I took readings and they do
not sit anywhere on that chart.  I'm not questioning the chart's validity,
but what can be the cause?  My measurements as of 9:30pm last night:
CO2 -  48ppm = 48mg/L
Alkalinity - 70ppm = approx. 4deg kH
pH - 8.0!! (should be around 6.5 according to the chart, assuming the other
values are true)

My other relevant data:  40gal mod to moderately-heavy planted tank (S.
American plant species) set up since Feb. 5th, DIY trickle filter,
laterite+flourite substrate, pressurized CO2 at about 1bubble/sec, PC
flourescents (48" 2x65W Custom Sealife BriteLite) 150w WeissLite, using
PMDD.  Temporarily, I have 8 black mollies.

Something is not right.  I trust the pH test kit because how can you mess
that up?  I trust the alkalinity (I think) because it is a titration process
with a very unambiguous color change.  I'm not so sure about the CO2 test
kit because it is a titration process with quite a very gradual color
change. (but it must be sorta close, right?)  If you examine the chart, it's
obvious I'm measuring something wrong.  Is it possible that my test kit for
CO2 is measuring CO2 that's not dissolved in the water, but only suspended
in the water column?  (No, I didn't think so either)  I am trying to
disperse the CO2 through my pump impeller, but many very very very fine
bubbles appear in the tank coming out of the spray bar.


- Lew