No problem Major. Getting differing opinions is the nature of the FAQ's and personally I always post just to give my 2c to the mix, never thinking everything I say must be always right- that would be way too much responsibility.
It's just been my experience that they don't last when dry, and (almost) everything I've read tells me to keep ph probes wet. All the cheap ph pens I used to buy came with a cap designed to store solution in them to keep the probe wet. It says on my Bluelab meter- 'if it dries, it dies'.
Regardless of the wet/dry conditions- a ph tester should last more than a month before screwing up. Should check the calibration though.
Major, do you think this soil mix he is using would be affected by feeding with a poor ph? Isn't soil somewhat immune to ph swings?
Good question - and I have no idea. I've never used Roots 707 (or coco). I read a little about it and it could be anywhere for PH. It doesn't mention lime or other PH buffer. I don't like that it is low porosity/high water retention. That sounds like the opposite of what we want.