I have had great success with blue and yellow tangs. On occasion I have had to resort to freshwater dips of TWO minutes. I read your post, and based on your involvement with this site I will spare you of Tang "ethics".
If you havent considered it, look into placing cleaner shrimp in your tank for when your fish clear QT. The insurance will be well worth it. After your dip (I hope, I hope, your not to late) consider feeding your new buddie some fresh veggies. Culerpa is quite the treat and legal if you live outside California. Good Luck
, I'm rootin for ya!