The white stuff on the skin that you are seeing can usually be taken care of (with FRT) by simply raising the water temp above 80F (about 83F). If you don't see any improvement in a week or two you can try a warm salt bath once a day (9grams salt/1 liter or water). FRT will usually take a variety of foods and are generally pigs (like their nose implies). They are not strict herbivores (nor is any other species of turtle). Try commercial turtle chow, sticks, fruits and veggies, dark greens (especially dandelion greens), shrimp, fresh water mussels.
And do visit a qualified turtle vet (if you have one in your area). Unfortunately, there aren't very many in existence. Good Luck!