Folks, if you've recently upgraded or renewed your annual club membership but it's still not active, please reach out to the BOD or a moderator. The PayPal system has a slight bug which it doesn't allow it to activate the account on it's own.
I'd imaging you can just scrub stuff off, I've never really seen a need to clean it though, it's not like a ph probe where it has a piece that needs to stay clean in order to read right.
Dip it in vinegar for a while, should wipe off after that, I don't see how that would damage it. Corraline also won't mess up any readings that I'm aware of.