How do I know when to replace my PH probe?

[MJAnderson]

Will it just stop working one day?

I've had mine for about 9 months.

[clp]

That is not a usual failure mode. Over time the pH probe will go out of calibration more quickly, or be more difficult to calibrate/slow to respond. If it takes more than a minute or 2 for the probe to reach its end point when calibrating, then it is probably time to replace it.

Curt