Guppies almost always seem hungry. They are livebearers and so their objective is to be born, grow fast and make babies as soon as possible. So they want tons of food.
Their nature is to eat what is available, which is catfish pellets if they already ate their food.
You might consider making a ledge which catfish pellets can go underneath and less easy for the Guppies. Though they can skinny into lots of places.
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves