With a little work they will be totally usable. The problems that might come up are more irritations if you treat them right.
First is that they are dirty and will have lots of loose stuff hanging on. You can brush them and spray them with a hose to remove what you can. There may be some still come loose once they are soaked but that means you might have to scoop some loose stuff out. Not a big thing for most.
Got a way to cut them down to size to fit your tank?
Get a container like a plastic tub to do a soak. There may be bugs and lots of things inside the old wood but a bleach water soak will let the bleach soak in and kill/sterilize most anything inside. Much like we treat plants with a dip only much longer as the wood is much thicker and takes time. Don't worry about killing this plant!!
A trash can maybe? Add 1/2 cup or so of the really plain cheap bleach that has no colors or scents added. Watch not to get the bleach on your clothes!!!! The bleach may turn the wood white but the color will come back in a week or so in the tank.
Let it soak at least overnight or longer so that it really soaks in. You may need some rocks, etc. to hold it down. When done soaking, take it out , rinse it to dilute the chlorine and then let it dry until you can smell no more chlorine. Sun will make it dry quicker. The chlorine gasses off as things dry.
Figure out a way to set it in and hold it where you want it and you are good!
Wood that dry should have no color or tannins to bother you.
Last edited by PlantedRich; 05-25-2014 at 03:33 AM.