Thanks for your help Shad!

As I said, I have had this QT running for 9 months now, and more fish have died in it than made it through. Until I set it up, I'd NEVER lost a fish. On the other hand, when I've added a fish straight into the main tank, I haven't had any problems.

I am in NO way suggesting anyone skip the QT process, but my own experience leads me to think that my particular situation with this particular fish may be leaning towards something else...