Mine were the same, very tough to get to eat sometimes.Yellows are some good looking fish but they were finicky eaters when I had mine.
I am planning on planting the tank to make it more the fishes natural habitat. All of those foods would be sufficeIME catching juvenile yellow perch, they like a lot of cover especially vegetation. I've never kept any in captivity. Would worms, Mysis shrimp, small bits of fish be good foods?