What to feed my koi fish?

i just got a koi fish and i had normal tetra fish flakes that i fed him, the thing is he will only eat them off the bottom. he wont come to the top and get them off the top. so i would push the food down so he would eat. Today i had purchased koi pelets (i was unaware they floated) well they float and he still will not go get them. should i look for a different food? or just give it time and see if he will eventually eat from the top? thank you for awnsers