What's wrong with my fish?

[Oilers]

Thanks for all the responses guys! I don't have a QT, however, I am in the process of setting up my nanocube (28G). I can use it as a QT but it might be too small. Also, if I treat him with medication, what medication do I use?

[George]

28 G is perfect for a QT. Go to a grocery store and buy a box of epsom salt and go to your LFS and buy a box of maracyn-2 and a seachem ammonia badge. Those will come handy even you don't need them now.
If the QT is not cycled already, you need to do water change more often and watch for ammonia.
Add epsom salt at one tsb per gallon of water to the QT. Epsom salt is pretty harmless so some people add up to 4 tsb per gallon. Start low and increase it up to 4tsb per gallon over a period of one week. If you do water change, make sure to add epsom salt back. Watch the eye to see if it's getting any better. If it's not getting better in 2 weeks, use maracyn-2 according to dosage on the box. Let me know if it's still not working after 2 treatments of maracyn-2. We may need to treat it for fungus and what not.
Good luck.