My bogwood occassionaly grows a fluffy, mould thingie on it.
Hasn't harmed any of my fish and in fact, the gourami and shrimps often munch on it quite happily when it does appear.
I did ask about it in the planted section when it first appeared - cos I'd lost other fish at the time - but no-one knew what it was. Tried to scrub it off, boiled the wood for hours etc, but no luck.
I have however taken to see it as an indication that my water stats are on the high side and do a major vac and water change whenever I see it appear again.