Peculiar spots I need some help with..

[Diver]

I think it's going to be hard to diagnose without some professional help (in the form of swab taking). Could be bacterial, fungal or even viral in addition to a possible reaction to a chemical or something. I'd definitely quarantine from the others until you know, surely swab testing can be done by vets in your area even if they don't treat reptiles and amphibians?