Of CO2 injection and pH

	Ive just started CO2 injection..using yeast/sugar mixture.
	Im getting a steady stream of CO2 from the airstone..which
	I placed in the water-exit tube of a gravel vacuum. (The
	bubbles get trapped by the flow of water and bounce
	around for a minute or two b4 combining into a big bubble which
	fights its way to the surface.) Neat huh?
	In three days the pH fell to about 6.4 from 7.0..so far
	no adverse affects on the fish...plants are showing 
	impressive improvments.
	I was wondering if the pH is goin to fall more..I dont
	want to be killing the fish. I havet got a CO2 test kit...
	they didnt have any at the store...gonna be mailordering one
	Im was using Bullseye 7.0 (which obviously gave up on me).
	Im also concerned about the purity of the CO2 being produced..
	I mean...it stinks...I was thinking of having it run thorough
	some sort of filter to clean it b4 bubling it in the tank.
	Any ideas/comments/experiances?
	Any information at all will be greatly appreciated.
	- Ghazanfar Khan Ghori