Acid buffer

Has anyone else tried Seachem's phosphate-free acid buffer?

I got tired of trying to use peat to lower the pH in my 125 gal tank so I
tried this acid buffer.  Over the last week I managed to decrease the pH
from 7.2 to 6.6, however, I found that the KH decreased from 6 to 0.75!
The GH increased a little from 5 to 7 dGH.  With the decrease in KH, my
CO2 concentration decreased from 18 to 7 ppm (measured using LaMotte test
kit).  I have yeast + sugar bottles (3) producing CO2 for the tank.

How can I increase the KH and CO2 now?  I don't really want to raise the
pH though - or is this going to be unavoidable?  My tap water has pH 8.2
and approx. 20 dGH and dKH (350 ppm CaCO3) so I use de-ionized water for
my water changes.

Any suggestions?