I use Reptomin floating food sticks as my staple diet, supplemented by ocassional fresh food, such as small red or leaf worms. The Mazuri floating sticks mentioned below would also be good. Beware of purchasing just any commercial turtle food you see in the pet store because some may be nutritionally OK but have very poor acceptability by the turtle. They are supposed to be slightly omnivorous, so you could try a few fruits and veggies, such as kale or collard greens now and then.