Did you add live rock, corals , or any other inverts since the last fish ? ex: shrimps, snails , slugs, starfish, urchins...? Where they quarantined?
Do those spots that we see tridimensional ( bumps ) or hollow? Beige-grey and moving? Any of those spots have a bloody centre or edge?
Does his poop looks normal?
Do you have a better picture with daylight possibly?
First look makes me think of flukes.... ?!!