This looks like a starry blenny and as the same with lawnmower, its a myth and belief that they are algae eaters. You can tell they are getting proper diet by looking at their abdomen, which should be golf ball shaped. A blenny with a pinched belly isn’t finding or receiving enough food.
Although this blenny needs algae to survive, its a belief that it can survive on algae alone and actually need to pound and gnaw on coral, ingest detritus and waste from the coral which includes coral skeleton, sand, gravel, and for meats - fish eggs and tiny chopped foods.
If a blenny is not getting enough calcium carbonate in its diet, it will rapidly deteriorate. To supplement, offer an occasional helping of algae-based wafers or pellets.
