It's like a forest of thick black hairs growing on the leaves of all my plants, like a kind of host/parasite situation. This isn't an emergency because all the fish are healthy, and the plants are still in good condition other than having this stuff growing on them. Water stats are all perfect (0,0,0). I am able to pull the black stuff off in clumps but it would take weeks to get every single hair. The various debris in the black hairs is accumulated food and faeces.