It barely dropped over a 4 day period. We've tried with air stones on, airstones off. New substrate, still too high. The only fish that can survive in the tank so far have been otos and giant danios. Everything else dies after water changes which bring the highest spikes. Even our kribs. Which really p/o'ed me.
See, and from what I've read, having the pH controller will keep the pH level, even with water changes. R/O isn't an option, the set ups are too expensive. The CO2
equipment I have came with a tank, the pH controller is the only thing I have to buy.