I always think the key is in variety.

A good quality pellet food like hikari or progold can be alternated
with a variety of fresh veggies and meats.

My list includes:

chopped cocktail shrimp
peas
broccoli
spinach
bloodworms (which are available frozen, dried, alive)
brine shrimp (also avialable in all sorts of ways)
daphnia (again there is a wide choice)


You can still use your flake from time to time but it makes a big
difference not relying on it totally.

I am also a great fan of algae on back and side walls. A great source
of vitamins.