I used 2 cups in a cannister filter on a 125gal tank. I have a Milwaukee SMS PH
controller on the tank and I've ben watching it carefully. The reading is displayed digitally and is accurate to .1. I know this worked for me.
I watched the pH climb gradually from 5.5 to 7.3. This took about 24 hours. After only a day the pH was stable and will vary from 6.9 to 7.2. Even with the injection of CO2
my pH is now constant. The KH
rose from 0 to 4. My feeling is that if you get your KH
anywhere from 4 to 6, you'll achieve a stable pH and it's what you should be looking for.
To answer your question about leveling the pH and cycling. It's an interesting question. I can't confirm this but I think a pH crash kills off the "good" bacteria. The bacteria will come back at a very low pH but, you'll kill it with your first large water change. Anyone else have any thoughts?