My daughter has just bought a 200 L tank and has added 2 pieces of driftwood. She has the correct size filter. Tha water colour is very brown and I presume it's the tannin leaching out of the wood. I have emptied the tank once and soaked the wood for a week hoping this would fix the problem but it's back the same as it was if not worse. Obviously we haven't put any fish in yet. Has anyone any ideas on how to get rid of the tannin out of the water other than not having any wood in there?