I would recommend ordering fish protector, vita-chem and garlic guard. 1-2 drops of each daily per gallon help heal fin damage as well as fight to prevent infection.
I would treat all water with both prime and fish protector, 1-2 drops of each per gallon. The prime will help with the
ammonia, but will be more effective if added daily since it's effect on ammonia lasts about 24 hours.
Stock triple sulfa and rid-fungus. If you want to treat for fin rot, use both as fin rot can have origins in either or both infection and fungus. Fish protector actually helps improve the effectiveness of antibiotics.
Thawed frozen bloodworms (Hikari brand is what we use) should be his diet. The protein helps strength his system.