Purigen will remove tannins from the water. I tried carbon, and didn't see any difference, though that may have been because the wood was still putting out more.
Now that ive got the mopani wood in my tank, it is developing a film around the wood. It is like a white'ish clear layer all over the piece. What exactly is this and is it good for the tank? Will this go away?
If the piece is small enough, you can boil it for a few minutes.
Sounds like fungus. It is harmless and will go away on its own.