was he eating for you before? if so what type of food were you feeding. if you have not tried it yet try emerald entrese its a frozen algae based food with mysis shrimp I thaw in a cup of water and 2 drops of garlic extreme at leat once a day veggie flake(omega one) in the am.check water parimeter make sure everything is in good levels ph nitrates sg ect.tangs are normally big eaters if hes not eating I would say something is wrong with either the fish itself or the water.ps if all checks out good and he still wont eat add 1 drop garlic extreme directly to your tank per each 10 gal of water the fish will absorbe the vit through its gills which may help entice its eating