Losing fish is hard on everyone, but it happens to everyone too. The trip from the reef to your tank isn't easy; but we sure have more success than we used to. Most online dealers are outstanding, I don't but livestock anywhere else. Because most online vendors ship from a wholesale facility right to you, the fish is actual handled & bagged less than a fish you get from the LFS. I don't know how big your tang is; but small nasos are very difficult to ship and acclimate; dealers & wholesalers lose quite a few of them. Just my opinion: I am not a fan of drip acclimation, although some online dealers suggest it for everything and some just for very sensitive fish & inverts. I seldom take more than an hour (usually much less) to get a fish from the bag to my QT. Ammonia and oxygen in the bag are my biggest concerns. The fish was eating, so be sure all of your parameters are in order and you have plenty of water movement & surface agitation. Tangs need lots of oxygen.