The Tahitian Butterflyfish requires plenty of room to swim, and a peaceful community aquarium of 50 gallons or larger. It may be kept singly; if kept as a pair, both fish should be introduced to the aquarium at the same time.
Its diet should consist of chopped meats such as marine fish, crustacean meats, or mysis shrimp. A vitamin formula with the meaty foods such as Vitality may help keep the colors bright. I don't know if you will have much success feeding it flake and pellets.
In any case, it is not the ideal fish for aiptasia control. Based on what it eats, I doubt it will even touch aiptasia. Look at Raccoon Butterfly fish instead.