I use a pH monitor from milwaukee. The bubble rate is quite high...on the order of 1-1.5 per sec. I have the controller set to pH of 6.8...it starts and stops as advertised....a 4-5 bubble rate per min which some people say just does not put the CO2 into solution like some guys state.
100 Gal Planted, two Filstar XP3, Milwaukee SMS 122 pH controller, Milwaukee reg/bubble, compressed CO2, reactor 1000, 7 WCMM, 12 Ottos, 14 neons, 1 SAE, 3 German blue rams, 2 Florida Flag Fish
10 Gallon...20 Endler's live bearers planted, peat/kitty litter/sand substrate
15 Gallon...Just Schultz Aquatic Plant soil