I have a 2 year old lawnmower blenny. He eats anything pellets, flakes, frozen mysis, brine, and blender mush, he also will eat algae sheets. They like more that just algae. Try getting some algae sheets for him. May have to soak in a garlic additive or i use Zoa by Kent marine, enriches the food and can entice to eat.
29g Mixed Reef, 150w 14k Phoenix MH w/ Moonlights, Reef Octopus BH1000 HOB Skimmer, Ecotech Vortech MP10es, ReefKeeper Lite (Plus), PH Probe, Temp Probe, ATO, Carbon/GFO Reactor.