Seal, no. You could add a large amount of chlorine, 1 teaspoon per 250 gallons of water, twice a day, for 7 days. FOR SEVEN DAYS ONLY. This will help to bleach the tannins from the water AND from the wood.
HOWEVER, other than the aesthetics of the brown water, tannins are not harmful in ANY way. In fact, tannins are added to a lot of tea, and some wines, to give them more color.