Blood worms.. in my case I'm allergic to blood worms so I fed mine wardley's shrimp pellets, they break up really small and are easy for them to eat. Had mine on those for over 2 years.
I feed flakes, blackworms, shrimp pellets, and even algae wafers from time to time. Mine seems to prefer live blackworms (freeze-dried work too), but eats sinking shrimp pellets regularly.