May I have some advice on prolonging my Fantail Goldfish Life?

You seem to be doing it right, use the fungicide with a LITTLE salt. mAKE SURE IT IS AQUARIUM SALT AS TABLE SALT CAN KILL THEM. iN A FEW YEARS MOVE THEM TO A 20 GALLON BUT ONLY WHEN THEY ARE LIKE 4 INCHES. sorry my caps locked on. Keep it up. As with the air.. put an airstone on it they are very cheap and will make the bubbles small enough to atually disolve in the tank. Hope they get better.