Worried about my goby - not eating

[Blinky]

I don't think it's an oxygen problem - I'm using an AC 70 (old model 300) as my refugium, it's got a baffle but the flow rate is still quite high, there's a lot of circulation and because it's a HOB filter the surface is constantly being broken. There's also a PH (AquaClear 101) on the other side of the tank.
I read for ages last night, I wonder if it was Amyloodinium - listless, not feeding, difficulty breathing, erratic swimming... the only symptom he didn't have is the velvety coating of yellow dust, but from what I understand it attacks the gills first and can kill fish very quickly. I hope it's not that, so far my wrasse looks okay.
Thanks for the sympathy guys, it helps
[Edit] OG, that's awful I'm so sorry you lost all those fish! It's funny, I never considered a virus. Whatever it was, I hope the wrasse doesn't succumb. [/edit]

 

[Max]

Eww, you don't have a hospital tank? I'd almost say do a f.w. dip in case it has parasites on it's gills . It might kill it in it's weakened state but, at this point you don't have much to loose.

 

[Blinky]

Sorry, maybe I should have added a new post rather than editing the second-last one - I euthanized the goby last night. It was plain to see he was beyond saving and I felt it would be cruel not to put him down at that point.
The wrasse is completely fine, looks happy as can be and is eating very well. My suspicion is that the goby may have been caught with cyanide, or been weakened by improper/under feeding at the store and succumbed to a parasite or virus.
I don't have a hospital tank, but I do have a Rubbermaid container, extra filters/PHs, a heater and mixed sea water standing by if they're needed. The goby crashed so fast I doubt there was anything I could have done - within the space of about eight hours he went from happy and eating to nearly dead.

 

[Blinky]

Argh! Just have to rant for a second...
I went into work today for the first time since purchasing the goby (I have another FT job, just work PT at the LFS), and told them that he died after days of looking fine and eating well. I expected some questions, but when I said that the levels are all good and have been all along (today's results are NH3/NO2/NO3/PO4 zeros across the board, pH 8.3, salinity 1.023), and that my other fish - which I bought from another store - is doing very well, the only answer I got was that I shouldn't have added the fish to a 'young' tank. This frustrates me, since two other staff members who know their marines and the details about my tank said he'd be just fine!
I could be wrong, but I don't think I made a mistake purchasing this fish; I think he was sick from the start. Incidentally, they had another of these gobies in the store when I bought mine, now it's mysteriously gone (and wasn't sold). No one told me if it died, they just ignored the question. Reinforces my decision NOT to buy fish at work.