Many folks are beginning to strongly question whether or not CO2 can crash the pH, or will it just drop it to 5.5 or so. One viewpoint is, as tazcrash69 posted, and the other is that the pH is not an issue, only the high ppm of CO2 is an issue for fish. My view is that I need to keep an eye on my fish and shrimp if I increase my bubble rate, just to be sure they are not uncomfortable with it. So, I have raised my bubble rate a little each week until I found that BBA was no longer trying to start up again on the leaves. My fish didn't seem uncomfortable, so I left the bubble rate where it stops the BBA. For my tank, with my method of introducing CO2, and with my water circulation, that bubble rate is around 3-4 bubbles per second.