So in my 20 long I have 3 fake plants and there is some grey stuff growing it's really short and sparse I do have shrimp I'm the tank and black molles which seam to eat some of it. But should a take the plants out and use peroxide and scrub it off. I dont mind how it looks and if the shrimp eat it then I dont mind leaving it. But I could be wrong about them eating it. Idk lol. My chocolate shrimp seams to spend most of his time on the fake plants eating. Non of my other shrimp seam to though.i will post pictures in the morning.