I usually feed my GFs the Aquarian goldfish food, which they love. I also have spirulina flakes that I am reeding about once a week, because I want them to have some vegetable matter in their diet also. But how often should I feed the spirulina, an ideas?
I do use flake food, but I soak it in a small bowl for about 10 minutes, then pour it into the tank.

I feed spirulina flakes every other day ^_^.

I usually feed w/ Spirulina falkes about 3times per week.

I feed spirulina flakes to my goldfish for their second meal of the day, at night. In the morning they get a different things. I'm using this up from my cichlids I used to have. After a while they will get it about 3 times a week.