Help!!! There's some white translucent thing on my wood decoration!!!?

I recently set up a new aquarium. It's going fine last week, now I'm in the process of adding the plants. But, yesterday, I saw some translucent whote fluffy coating on my wood decor (it's a mopani m from JBL brand) I immediately remove that piece of wood from my tank. But today, I saw the same translucent thingy growing om my thermometer! What's wrong with it and how to remove it?