My box turtle has skin issues

by John Magellan
(Albuquerque, NM, United States)

My Southwestern box turtle skin is dry. I have tried keeping the humidity up and change his water tub every day. I have also been using purified water to make him hypertonic to the water, but im not sure if thats helping. On another note, he has developed this hole in his skin on top of his head. Im not sure if that has to do with his skin being dry, or if it is something else entirely? What can I do to help my turtle.