I am glad he is eating and doing good. He is new so he might like the pellets later on. So i would still try to offer them to him , but remove if he don't eat them so they don't sink to the bottom and contaminate the water I am saying it because flakes cause swim bladder issues more readily than most pellets. And flakes also muck up his water quickly. So i would offer him to see if he would like them later. And pellets are better in general any way especially if you can find high quality protein based pellets with the first two or three ingredients as whole fish not fishmeal or wheat( Omega One , New Life Spectrum) Blood worms also can cause constipation so feed them as a snack about 3 times a week.