Well, I think that we have to understand what these/most fish go thru before we get them to our tanks.
From collection to mass storage facilities to packageing and shipping around the world to shipping to LFS and going from tanks to tanks and different water conditions to different acclimating.......
You know, IM suprised that any of them live.
The long term stress does slowly weaken the ammunity systems that allow the ick, ect to florish and eventuly it takes its toll. Sometimes they are like this for weeks before we get them.
We put them in our tanks and do everything right and our water is perfect and tank size is good and we cant figure why a week later there dead and what did I do wrong. Maybe you did nothing wrong. It was just overall too much for the fish to take. And I not knocking QTS its just that they are one more step in the prosess.
Like ophiura indicates, Tangs are among the most sensitive spc. and among Tangs the regals and powders are.
I got two hippos and a powder blue when I first set my first tank and the powder didnt make it and the Hipps did 3.5 years later, I still have them.
I beleive that you can NOT say one is hardier than the other and its just that the powder had been thru more stress befor I got it.
I just felt like I had to say this and dont think Im knocking the hobby because I love this hobby and no one is born knowing any of this stuff so.........
That,ll be 2 cents please