I built the Rex Grigg reactor in order to better disolve the CO2 in my tank. Out water here comes out of the tap with a pH around 7.8. I have been running about 2 bubbles a second and it is not going below 7.1. I had been told that for a 72 gallon that 2 bubbles per second should be enough. I have bumped it ip to 3 and it still stayed above 7.0. All I have for filtration is an Eheim 2217 and nothing else for water movement. The reactor is on the outlet side of the filter. Any ideas?