> Lots of comments/hints from list members but nothing that really rings a
> bell. I always mistrust meters, pH probes and solenoids. The probe might
> have gone wacky and somehow given your tank a wopping dose of CO2.
[snip]
For people using a controller, the proper way to set it up is so that, even if
it is stuck in the open position, the pH drops only a little lower than your
normal desired setting. The controller will still regulate, and some safety
margin gets built in this way.
-- Stephen