thats the spiney boxfish not the burrfish ..which your lucky with..he will get more rounded as he grows a very docile fish ...well could be a loss of slime coat from transition to the captive life.. well hes in his own tank thats a good start..I dose all newcomers with melafix for 3 days.. this helps relieve stress,promote slime coat and help with any bacterial or fungal infections that they may have ..yes I use this stuff for everything, because its mild with no ill side effects that Is natural with no harsh chemicals. have seen no bad reactions in several yrs of use..how big is he about 2 inches?i see you have crushed coral with him thats a plus..they tend to pick up the small peices of rubble in their mouths and then spit them out.. mine did this all the time. helps keep teeth filed.. while hes not eating dose the tank with selcon he will get the nutrients from this through absorption of the gills you can also do the same thing with the garlic stuff your using.personally i prefer garlic extreme because its more concentrated than garlic guard.if you have noticed him picking at the cc on the bottom you may even want to try spectrum pellets..large pellets.. they sink to the bottom.. for now hes going to a nocturnal feeder until you get him adjusted to your feeding schedule for now try morning and night just before lights off.. if you have moonlights for that tank it would be good to use those this way you can view his movements in the dark..good prepackaged foods for him are as followed
squid yum yums, plankton cubes,mysis,frozen krill and prime reef,formula 1.. silverslides
store baught would be all raw . scallops,shrimp,squid ,halibut,flounder,real crab,try to feed him daily.. feel free to ask anything else on him..