In theory, any flake food would suffice, if enough got beyond the top feeders for the middle and enough past the middle for the bottom dwellers.
In reality though, no fish would suvive on just one type of food, so a mixture is usually best.
Try some flakes dropped on the surface for the top, some dropped just below the surface for the middle and some pellets for your bottom.
Try alternating food types too, some shelled peas, or cucumber for the guys at the bottom, or live food will please (mostly) anyone!