All of what you said makes sense. I do have an acclimation box, a good one (elite aquatics). I didn't want to use it since I figured it wanted to be in the sand.At this point, I would looking at the lfs as the possible cause even if they're supplying fish that eat and swim around. That's not entirely indicative of overall fish health and sometimes you'll get brand new fish that are more susceptible to shock after something as trivial as a water change if the temp or PH of the new water differs enough from your display's parameters. You just never know if they have some weird bacteria that medicated QT would have taken care of. Also, fish do act differently when we're not hovering around the display. I've added fish and watch them swim around perfectly fine. In the morning, that same fish would be in the top corner of the display with ripped fins.
I think I'll wait and stew before I add another one. It was a gorgeous fish. But I don't want the same issue happening again. Most what I read is that they're difficult because of eating habits. Once you get them on frozen food they're just as hardy as other wrasses