he looks really emaciated. see how he is pinched in behind his skull? and how pinched in his tummy is? you bought and ethiopian lemon. my reccomendation is call your lfs and see if theyar ewilling to honor a credit. idealy it would be nice if they would still give you a shot to get him to eat (although at this stage he is already deteriorating his organs) but give you a credit if he dies.
this happens alot in the saltwater world, and is sort of the dark side of the hobby. very few fish adapt well to captivity. i see it all the time with puffers with "stuck in a box syndrome" it breaks their little brains to be stuck in glass cages. either the suck it up, learn to adapt and become well adjusted little fishy citizens, or they become highly neurotic, panicky, and starve to death or jump out. it sucks but it is true.
your best bet is to keep the tank lights dim, water parameters high, and quit grabbing him with the dang tongs! feed the tank mates as you normally do, and offer nori rubberbanded to a rock not an algae clip. you can try garlic, but i havent had much success witha fish this emaciated. if you do get him eating, try soaked mysis in metronitazole to get rid of all those nasty internal paracites.
and pleas next time you go to the fish store, LOOK CLOSELY athte fish you are purchasing, find out how long it has been in the store, what it is eating, and NEVER BUY A FISH THAT IS NOT EATING! you must see with your own eyes that fish enthousiastically go after food before putting a dime on it. i hope you dont lose him, good luck