From my experience with drift wood it can take a long time to soak all the tannins out. I have some drift wood that I harvested myself from a local pond and I soaked it for a month doing regular water changes, scrubbed it with a toothbrush, and boiled it a few times, and it still made my water cloudy. It all just depends on the type of wood, and its age, on how long it will take. I have read that tannins in the water will not negatively effect fish, but I may be wrong. I finally was able to add my driftwood to my tank but I believe it took about four or five months to process it. Although I have some driftwood that I have bought from a LFS and it never needed to be soaked and didn't leech any visable tannins.