is it real wood or fake? If it is real you can boil it for an hour or so I have done this it didnt sink at first but i used a small rock to hold it down in the tank. It became water logged and heavy in about two weeks in the tank.
If you do get any discoloration, fresh carbon in your filter should take care of it. I have one piece in with my betta that leeches tannins like mad between water changes, but the betta loves the "blackwater" and I like the look.