Thales said:If you wanted to do everything you can for the fish you would put him in a QT tank, figure out what is actually wrong with the fish, and treat accordingly.
If you don't want to do really figure out what is wrong and treat, feed the crap out of him (which you should do for any new animal). As many times a day as he will take food.
You have a Q-tank and it's the one it's in. Don't add any more livestock to it for quite some time now.
Food = good because having a few extra ounces on the fish for when it really gets bad is only going to help. Then you won't panic as much if it drops off the feed for a while.
Lots of good water changes, keep toxins low.
Oh yeah - don't panic. Hard to do but keep a level head. Give the fish some space.