with guppies, im not sure, I know guppies eat flakes by the butt load, you can feed them brine shrimp and worms too. Try to give them some stuff with carotene (Sp?) in it so that it will hopefully enhance the color of your fish once they eat them. But basically, any high quality flake food should work......Guppies are obnivors so your options on feeding them are endless, they can actually make a nice display too if you set your feeder tank up accordingly. Maybe a childs tank of something.