Well I've never kept them before but I would still raise the water temperature up to 85 degrees until your turtle looks and acts better. What all do you feed your turtle? Sometimes diet plays a role in RI. Some species get it from not having enough vitamin A in their diets.
http://www.austinsturtlepage.com/Care/caresheet-fly_river_turtle.htm
http://www.austinsturtlepage.com/Care/caresheet-fly_river_turtle.htm