FML Dying fish

[Aquattro]

The cyanide theory would get my vote as well. Sometimes this just happens. I had a powder blue do the same thing, lasted a month. I fed it fresh algae, it still shriveled and died.
I have another PB on hold at ProReef, it spent a while in quarantine, then into one of the large frags tanks for the last 5 or 6 weeks. Although it's eating was sketchy for the first month, it's still in great shape, compared to the one I had that died after a similar time frame.
But FWIW, I would never add a tang to a QT, the lack of real world environment seems to stress them out. I add them to the community, they get to hang with other fish in a reef, and watch the others feed.