Jan 19, 2013 #1 Catfaceskates Aquarium Advice Activist Joined Dec 28, 2012 Messages 123 Grey stuff on some rocks and sand bed?? Attachments image-2160484972.jpg 134.2 KB · Views: 79 image-994136579.jpg 106.8 KB · Views: 59
Jan 19, 2013 #2 ccCapt SW 20 & Over Club Joined Mar 15, 2004 Messages 5,365 Location Northeast PA Can't really tell with so much blue in the lighting, but I would guess cyanobacteria.