My turtles have white yellowish marking on top of her shell. They are hard, not soft. She started shedding and the yellow markings appeared under the shed. Underneath are white dots, which look different from the other markings. I have tried gentle rubbing them off with a cloth but they are part of the shell and didn't come off. We have a basking light for them. They are adult turtles so we feed them mostly kale, spinach and dark greens. And their tank is cleaned weekly. They behaviour normally, eating, basking, spends most of their time in water. I'm worried it might be some kind of shell rot or fungus. I'm asking for advice on what it might be. There are no turtle vets in my area so if I have to take them to someone it would need to be a serious problem.