I have this beautiful piece of driftwood that has this cottony white stuff growing on some parts of it.I have had it for a few years now and I first saw this stuff about a month after first adding it to my tank.I removed the wood and scrubbed it down with a green pad and left it to dry and just about forgot about it.Fast forward to about a week ago when I placed the wood in a tank for soaking so I could use it for my main tank and this stuff has crept up again,after all of the time that has passed.Does anyone know what this stuff is?