2.5 gallons minimum per fish., get some plants for them or they'll be bored and might start tailbiting, which is a bad habit.
Hold off on feeding him for a day or two, add 1 tsp of epsom salt per gallon. Premix it before dumping it in the tank. How many pellets are you feeding him each time? Max is probably around 8 pellets a day. Maybe try feeding him 2-3 pellets twice daily after he gets over the swimbladder issues and fast him for a full 24 hours once a week. If swimbladder is a constant issue, you'll need to play around with how you feed him and how many times you fast him.
If he gets sick again or you need more help, try posting in the Diseases and Emergencies forum for faster and more knowledgeable responses.