feed lots of algea to the tang, live macro is best if not then nori works well also just try to keep some in the tank at all time for the tang to graze on. your display tank now has ick and the only way to get rid of it is to let the tank go fallow (no fish or inverts). or you can do like many others and just feed you fish a variety of foods, i believe live is best but if you use frozen then add a little garlic and selcon. garlic is for appetite ans possible immune system help and selcon is vitamins.