Heat, salt, bubble wand, melafix, and pimafix. I would only recommend this because you are considering killing it. It must be really bad to consider this option. The pima and mela is just to help stave off any secondary infections that can happen. If the fish already has secondary infections like fin rot or fungus then you will need to switch to an antibiotic.
HITH isn't too bad and can be stopped quite easily by changing the diet and providing plenty of air.
If you really need to, go to any pharmacy and get some baby vitamins. They have all of the essential vitamins that you will find in every good fish food.