I have had problems where my CO2 was not affecting the pH of my tank even though I had 2 bubbles per second. My pH would never get below 7.4. Someone told me that I had to much filtration on my tank and that was what was causing it (I have a 72 gallon bowfront and I was running a Ehiem 2215 and 2217).
I turned off the 2215 and now my pH is at 6.3 which makes me happy. I would like to get a little more water movement by getting a power head since I had to turn of the one filter. Do I need one rated for 70 plus gallons or would a smaller size be better. I appreciate anyones input.