American green tree frog skin disease?

[rikkitiger]

My tree frogs are normally fine, i have had them for a month and a week as of this tuesday, and i have a slight problem. I notice this is not always, the skin sometimes looks like this. Just one frog. There is nothing it could eat like pebbles or bark or moss. There are silk plants.

So is this ok? I notice it goes away for a couple days then comes back. It may just be where he sits, but to be sure you know.
it is sorta light brown with darker brown spots. Nt like, three spots, kinda a little collection. Only on her back, too.