I have mopani wood. It grew white fluff at first, but every week I took it out and scrubbed it with a toothbrush in salt and hot water then rinsed it really well. It took some time to go away but I think it is gone.
Did you boil it? Most wood leeches tannins (makes water look brownish) but that doesn't hurt fish. It will also stain a pot if you do boil it.
Where did you get the wood?