Simpte 27

I recently went out and purchased a cpl of wooden diffusers by coralife. The bubbles are great! Nice really fine mist which rises to the HOB outflow and then get dispersed throught the tank. My ph doesn't fall, and thus my co2 levels are staying the same? I figured that my initial water parameters were way too high (ph almost 9 gh 38 kh approx 1 With r.o. and distilled water I got the PH down to 7.2 gh 7 and kh 7. How can I get more CO2 into the tank? Do I need to add a bell for the diffuser? Any help would be appreaciated.