Just bought a used Apex and I'm not going to use it for about a month or so. How should I store the probes? I've read a lot of different things and would like to get a consensus.
If they still have the caps, I'd get some probe storage solution and store them that way. If not, and you don't want to get new ones, I think it's ok to store them dry, they just need to be recalibrated before you use them. I'm not 100% on that last part so hopefully someone more knowledgeable comes along :)
The pH and ORP probes must be stored wet. If they dry out they will not recalibrate and the glass membrane on the probe (the inner glass tip) will need to be regenerated (http://www.all-about-ph.com/ph-glass.html). Storing the probes in RO water or anything else is not recommended as it will cause issues with the membrane.