Yay, a new frog owner!
Hmm, I would not bother with meth. blue or salt or anything else. Frogs are very different than fish and it won't be good for them.
That said, the conditioner you use for your fish is fine for them.
Sickness.. the most common thing is chytrid fungus, if that occurs you won't be able to do anything about it, sadly.
If your frogs make it past the 3 month mark alive, then you shouldn't worry about chytrid for them.. that said if you want to add to the frog colony, all new frogs must be quarantined for 3 months.