chickens love failed cheese, too!
I don't use a pH meter and have good luck with my mozzarella by using the spin test that Fankhauser gives directions for. If a one-inch curd won't spin in 170 degree water, then the rest won't, either. Just give it some more time to acidify. If it is getting late in the day or you need to do something else, put the curd in the fridge to slow down the acidification and get it out a few hours before you plan on spinning it.
Good luck and let us know how your further efforts go.