What is this in my reef tank. Dark maroon velvety growth on rocks only. When top removed is white beneath. I scraped a bit off previously & area regrew. What is it & should I leave it on. Tank been set up over 3 years all parameters spot on. White bit ...now lavender colour which seems to have a starfish in centre as I’d which bit can be seen on photo to right of centre
Sorry thought pic had printed. The growth is almost black & velvety to touch. Once removed, white area is soft but regrows black maroon within days. It’s not coraline.
Will leave if it’s not a problem. Over to you