Fungus on wood

[Kristen]

Does anybody know what this fungus is and is it harmful? I found it in my tank today while checking on my moss growth. Its only showed up in the past 3 days (thats when I put the plants and the moss in). No animals are in the tank yet. Im going to get the moss to grow out before I do
Its completely covered the ends of the wood, I mist the tank alot so the moss wont dry out (I have no lid to the tank yet, the previous lid smashed)
Its white and kind of cushiony.

Thanks, Kristen