A few pellets a day, about 3-4. Over feeding can lead to swim bladder disorders, bloat or constipation, all of which can be deadly.
Try switching it up with the occasional blood worm, brine shrimp or the inside of a cooked pea.
The brine shrimp and pea will help to act as a sort of laxative, to help them keep things moving through their system nd prevent blockages.
Best of Luck!