Actually, the tannic or tannic acid is rather harmless to the fishes, it is just that the water will turn unsightly brownish yellow. I have 2 driftwood in my tank now and what I did was to clean them with warm water, it kill off any insect eggs or bacteria as well. I then soak them in water, and after a few water change, they are ready to be put into the tank and don't leak any tannic at all. It is said that using activated carbon in the filter will reduce the tannic effect.
I read that some members here boil the wood, so you might want to read on their experiences.
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