Purple Firefish in QT, now an ammonia spike (despite using a seeded filter!)

Final Update

Well, thankyou all for the help along the way. Unfortunately, poor little guy passed away this evening. I figured things weren't going well, with him not eating at all. But still, he was my first saltwater fish, and I had hoped to hang onto him for a lot longer than one week. At the very least, I've learnt a great deal over the week, and will not allow things to repeat themselves once the QT is properly running.

On a side note: Double2mk, I have 2 koralia 2's providing circulation in my 35 gallon tank (with one aimed quite steeply upwards to provide a great deal of surface agitation). I also have a Deltec MCE600 skimmer which provides additional air-water contact (it is rated for a much larger tank, after all). pH has been pretty consistent at between 8.2-8.4, so I know CO2 was not a likely issue, as that would probably bring the pH down to more acidic levels than what I'm at now. In any case, I'll be chasing up an O2 test kit in the near future, just to rule that out entirely before I even think about putting a new fish in QT.

Anyway, thanks again everyone. I appreciate all your help.

Vale Phoenix.