I'm not sure in all honesty. I think that if I had done nothing, they would not have made it, but in hindsight, I think it was Ich and something else. I don't think that the hypo killed them directly, but maybe it caused other issues? The Desjardini Tang had some weird markings that I almost think was bacterial, but I've shown it to three LFS
that have people with lots of experience. They were all stumped.
I've done hypo in smaller QT tanks before with no issues. In fact the Trigger is in a small tank with a green Chromis in hypo right now. I'm working on bringing the salinity up slowly now and both look great. The DT remains fallow.
I think that right this instant, if I had it to do again, I probably would have tried them split up between smaller QT tanks and started the fallow DT at that point. If Ii knew there was going to be all the weirdness, I probably would have tried copper, but I typically go hypo.