Do you see any holes in it like a sponge? I’ve seen pics of large brown sponges in the ocean but not in someone’s tank.Any other ideas on this? In the photo, it appears to be above the surface of the rock, This is an illusion, the growth is tightly adhered to the rock. If I want to remove it, I would have to scrape it off..
Sort of similarNo holes it it. My first thoughts when it appeared was algae or sponge but I haven't found a picture yet that comes close to what I see. I'm sure there's a picture out there somewhere, I just haven't been able to find it. It began very small and has grown now for about 5 months.