While there are some good flake foods, most are not the ideal main food for reef fish. A variety of frozen foods is better. Cyclops, Calanus and Mysis are the best. Brine shrimp should be limited for various reasons.
Cyclops, Calanus and some other foods can be found freeze dried. Those are still better than flakes and a bit more convenient.
There are also some decent pellet foods for marine fish.
How does the fish behave? Any signs of discomfort?