make sure your tank is mature as well, 6 months or older. if it isn't the tang will surely die. also make sure you have a good current in the tank with lots of oxygen in the water as these guys live in parts of the ocean where there is lots of oxygen in the water. also feed these guys lots of veggies like seaweed along with , spirulina and if you can get them to eat it formula 2 of ocean nutrition whether it be the pellet or the flake. it also helps to have live rock. i would also keep the salinity down to 1.019-1.020 as this will help it from getting ick. have plenty of hiding spaces along with plenty of swimming room. tank should be no smaller than a 90 gallon.