I have a large 180gal tank. To add enough CO2 into the tank to drop the PH by 0.8 or more the bubble rate in the bubble counter on my regulator is too fast to count the individual bubbles rendering the bubble counter useless for any thing other than an indicator that the gas is flowing. I use one of the clear gravel vacs attached to a power head as a diffuser with an air stone inside it. I just watch the amount of bubbles comming off the air stone to make coarse adjustments to the CO2 and verify that the gas is flowing. I then use PH measurements taken over several hours to fine tune the amount CO2 and maintian a constant level. I don't bother to refill the bubble counter after the water evaporates.