on one peice of mopani wood a strange black hairlike growth is covering it but no other peices of wood just the one wat is this and how do i get rid of it
I suppose you could take the driftwood out, scrub it, and let the algae dessicate to death. That's what I do with my rocks when they grow too much algae.
I have something similar on the back of a piece of oak that I collected myself, it has not caused any problems and the water chemistry is fine so I just let it be.