It should be fine to put in your tank. I usually boil mine or pour boiling hot water over it just to make sure its sterile. If its one of those pieces of wood thats plastic all you need to do is give it a rinse. If it's a real piece of wood, sometimes leaving it in a bucket of water for a couple weeks helps it sink better, but than again if it has a piece of slate attached to it it should have no problem staying down.