Some dry docking and light cleaning... from atp:
This is not an uncommon sight in some species. This is your classic skin fungus. Not taken care of, it can enter the blood stream, become septicemic, and destroy certain organs within the body.
Note: The dry-tank method has yielded the highest success rate.
Remove turtle and place in a quarantine tank. The infected areas should be cleaned. Be careful when cleaning out the injury as the infection may have gone deep. Going too deep can cause extreme pain to your turtle.
Listed below is a regimen that I have followed in treating shell and skin problems and has yielded great results. While treating, you are looking for signs of healing and this may take several days before you can actually see a difference. A good idea is to take a clear photograph before treatment and compare it to another photograph of the same area a few days or a week later.
1) Clean infected areas thoroughly with a strong, undiluted betadine, iodine or Nolvasan solution. Let the turtle air dry in a warm setting for about 45 minutes.
2) Apply a generous coating of Silvadene cream. Work into problem areas. Neosporin is also an acceptable alternative (Polysporin for those keepers in Canada).
3) Leave the turtle dry and warm, ensuring that you do not over-heat, for 18-21 hours each day.
4) The next day, gently clean the affected area with a one of the previously mentioned solutions.
5) Place them into fresh, clean water. Let them swim, drink and eat for approximately 1 - 1 ½ hours.
6) Repeat procedure from Step 1.
This treatment performed daily or twice daily, should show you improvements within a week to 10 days.
NOTE: The betadine bath's 'weak tea' solution is not advised as this can potentially bring about health issues later on.