What do I feed my aquatic turtle? And how often should that be?

I just got a turtle two months ago. I have been feeding him these "Aquatic Turtle Food" (they're pellets). And that's it. I'm not sure if I should feed him anything else. My friend feeds her turtles minnows. Should I do that too? And if there is any other thing that i should feed him, what is it? I love my turtle very much and want him to live for a long time. So if you know anything about a turtle's diet, please respond ASAP. Thanks for all the help! :)