My yellow tang isn't yellow and has some new markings! Help!!?

he's pale,a sign of parasites.the marks on it are scratches,another sign of parasites.the redness is a secondary bacterial infection.is it eating anything at all?.he should have been placed in a hospital tank and treated with ionic copper(seacure).nothing short of a miracle will save it now.soak food in reefplus by seachem,vitachem,or selcon.(vitamins)and feed a variety of foods.for the infections you need a antibiotic (gram negative,and gram positive)and half the time they don't work tangs need very clean well established tanks.set up a hospital tank,for future use.if you want marines you're gonna need one.never buy a fish that just arrived at the store.the store should have had him a few weeks at least.did you have it a month or less?a month or more it should have adapted to the environment by now.unless the damsels were bothering it.