We have a RES over 5 years old and appears very healthy. Lives outside in small pond in Florida. His shell has a small spot that is turning white. The spot is hard and does not smell, it's just white. We've tried for weeks scrubbing it with a weak iodine solution, and keeping him dry for an hour each day. Any ideas as to what this is? I do think it's getting larger. I have pictures but don't think I can attach them.

THANK YOU