Yes, I agree with KK, there have been discussions in the past that it is really the *change* in pH (the delta if you will) that the autotrophs are responding to. Dave Spencer and I had some discussions about that because even in very acid tanks the bacteria will slowly come back to working even if they stopped working when the pH first dropped down to being very acid.
I also think our "graph" from Tim Hovanec of pH and growth rate have been good over the years that growth is stopped, stalled or very bad down at 6.0 and moving up to stalled at 6.2, then gradually getting better as we head up through the 7s until we finally reach the peak plateau of 8.0 to 8.4 where his lab work always found it best. Then the growth rate falls off a little as you go above 8.4.
My thinking has also gone along the same lines as KK in that I've always thought it would be interesting to do some fishless cycles where large water changes were done fairly frequently throughout the second and third phases when all the bad things (nitrite, nitrate, nitric acid) can and will build up. So you'd be removing those and replacing them with fresh tap water that has the things the bacteria want (ammonia in the right concentration, oxygen, calcium and other trace minerals from the fresh tap water.) It could be that KK will do one of these, she was going to try some "experiments" a while back.
Of course, two of the counter arguments are that first of all one of the supposed benefits of fishless cycling is that you *don't* have to change a lot of water like you do in Fish-In (especially if you stumble in to Fish-In unplanned and are overstocked for it) and of course the other one is the "disturbance" to the bacteria when a water change is performed which in some cases can cause the bacteria to "go on strike" for a couple of days in protest.
I truly don't know: it could be that a bunch of disciplined water changing with careful recharging of ammonia and bicarb to bring up back up to 8 would really shorten a fishless cycle significantly OR it could be that the darn things are just going to take their set amount of time to grow and that's it! All our hunches are made very hard by not knowing how many bacteria a fishless cycle started with from a particular tank of tap water. That alone is an exponential factor and a constant confounder for all our "hobbyist" experimenting!
~~waterdrop~~ (gee, are we having fun now
)