I made the mistake of making my reactor so the CO2 bubbles were very large, over 1/4 inch in diameter. I introduced the CO2 at the bottom. The big bubbles would shoot to the top and collect there, making the reactor less efficient than it should be. Recently I modified it to get much smaller CO2 bubbles, entering near the top. Now the bubbles hang suspended in the middle, swirling around and around. So, the size of the CO2 bubbles makes a difference, as well as where in the reactor you introduce them.