I have a nice piece of driftwood, that barely fits in my 75 gallon that has not stopped leaching tannins. I soaked it for at least 3 weeks in a utility tub and then got impatient. I have been doing water changes almost every other day just to make the plants viewable. This has been going on for about 3-4 months. Its too big to boil, so what can I do to make it stop?