Andre Malenfant wrote:

The Ph will not drop if your kh is high (or less).


Andre,

Perhaps we have a misunderstanding (or a missing word?), but the point
above appears to be wrong. Injecting CO2 will drop the pH no matter what
the KH. You can read all about it he

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm