I have a rash on my arm from cleaning SW tanks at work thats been there for months. Its on the crease of my arm where it would rub against the tank edge. It has been the same size the entire time, but if it comes in contact with tank water, it immediately turns red again and itches like crazy. I've gone to the Dr for it, but he gave me a cream to apply twice a day but he said if even a small amount of the cream got in a tank it would kill everything.
I have yet to use the cream lol.