He is just adapting and acclimating to his new environment. In a few weeks time or so he should get used to you approaching the tank and come out associating your presence with food.
Mine is over a year old and will eat anything. Algae, brine, mysis, flake, pellet, plankton, blender mush w/ shrimp, oysters, scallops, and talapia. He loves it all and hes the hog of the tank.
Here he is just chilling out in the mid day sun.
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.