pH meter uses

[Tom Turophile]

I'm trying to price out pH meters -- Extechs, Hannah (any others?) -- and I'm wondering -- how many uses can you get out of them before you need to replace the electrode or refill it?  I don't really even know why you would need to replace it, either...

[sigurdur]

I don't know how many uses you can get, but the electrode erodes with time and usage so it all depends.
You can expect replacing the electrode at least once per year.

Some meters allow you to store the electrode in a buffer solution so the lifetime of the electrode increases.

You need to test your pH meter regularly (I'd test it before each use if you don't use it many times per day), at least in the start of each day. You can adjust most, if not all, meters.
You use two buffer solutions to test and adjust your meter, pH 4.01 and pH 7.