Thank you for getting back to me. This sounds like an infection of the shell. There are several different ypes, but treatment is the same for all of them.
The most effective involves what is called 'dry-docking.' You'll need to prepare a 'hospital' for Athena. A large plastic tote works well. It should be equipped with a basking area at 90*F and a UVB light. The turtle will be kept warm and dry, except for a 30 minute bath twice a day. The two baths are very important to prevent dehydration. Feed her during the bath. After each soak, scrub the shell with a clean toothbrush with Betadine (available in drug stores) on it, but try not to get it on the skin, and especially avoid the eyes. Do this twice a day. Follow that with a coating of anti-fungal cream (the kind sold for women to use to treat yeast infections). These measures may be enough, but sometimes more is needed. If the problem doesn't clear up within two weeks, you'll need to have Athena examined by a reptile vet. These links will take you to directories of vets:
Make sure your UVB light is under 6 months old. An older one that no longer emits enough UVB can contribute to shell problems.
If you have more questions, let me know in a REPLY. I hope Athena will be fine.
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