A bit at a loss to explain this. From 1:30 to 2:00 today my ph dropped almost a whole .1, and an hour later, climbed again. Nothing unusual going on, the sump and top-off are at normal levels, so it wasn't an ATO dump, the power didn't go out, no one was home to open or close any windows or turn off the ventilation fans. There is no dosing scheduled mid-day either, that all happens overnight, and has for over a year.
Over night there was a water incident in the condo across the hall, so at some point today there was an industrial dehumidifier put in the hallway to dry the carpet, which may have some effect on the humidity in my place. I'd expect a change in humidity to have an effect on my top-off water, not the pH in the tank. And a drop in humidity wouldn't have allowed a 1 hour recovery.
Any ideas?