What exactly is the white stuff covering? Is it on pieces of wood or on all
surfaces? Is the white stuff "fluffy" looking or more like a powder?

The reason I ask is that on newly introduced pieces of drift wood, it's not
uncommon for a white fungus to temporarily appear. The stuff is harmless
and usually goes away on its own after a week or so. If it is anything
else, I will have to let some other more knowledgeable answer that one.

Marlin