Might that be Mopani driftwood? Ive got two pieces.....one has this stuff on it, theo other....none. Separated my maybe 10" in my 75 gallon tank. I remove what I can with a toothbrush. My Oto's, pygmy cories, and Sakura shrimp havent touched the stuff.....maybe they have better things to eat?
Ive had it on that one piece since Ive started the tank, maybe 6 weeks. I do inject CO2, and do weekly 50% water changes.