Use new, high quality activated carbon and remove it from your filter after the color is reduced to an acceptable level. They also almost always need to be weighted. I agree with Tom Barr's assessment as to what to do with wood you are unsure off. Healthy seaside trees killed and uprooted by a sudden rise in surf. The surf slaps some about for so long all their bark is ground away and tannins are thoroughly leached out.
Some pieces get a barnacle or two.
Most that remain emersed grow seaweed. Some surf is mostly industrial and while its waves will leach out discolourng tannins they allow the trees to absorb industrial contaminants. These are factors that can affect the safety of your driftwood. Hawaii is in a similar situation. Yet even here there are relative areas of safety.