If the rash goes away within a few days every time you do not need an antibiotic. A bacterial infection almost always needs several days incubation before breaking out.
I would also doubt stray voltage for a diffuse rash.
It is much more likely that you are mildly allergic to something in the tank. I know of one woman who works in a LFS who is allergic to one salt mix. She switched to a different salt mix and her rash resolved. There are also corals which release toxins. The suggestion about gloves as well as antihistamines ("anti-allergin") areis also good ideas.
Go ahead and post a picture.
Anyone who is squeamish should stop reading the thread NOW.