I find if i keep watering them, my frog tank, also, I get fungus problem. I just let the substrate dry out a bit and not over water it. As long as they have a source of water and not bone dry, I think they should be alright. Besides, I think in the wild they also seek dry area not just the wet the one, or you can just soak them yourself. Also, the good turtle food helps their skin a lot, so I include as part of the diet.