I think the biggest mistake was not QTing the RT first. If you have only had him for 2 weeks, IMO, he should still be in QT, but it's too late, so you should treat your entire tank.
There is no telling if the other fish contracted anything or not, so better safe then sorry.
As for not eating like the others... My Jag did that after I stopped feeding massivore, and started feeding cichlid gold.. he refused to eat it.. But, he ate it when he got hungry enough, and now he's a pig. But, drop in massivore, and it starts all over again. haha.
Leave the lights off for a week, and treat your tank. I think everything should be ok.