Hi and welcome to Aquarium Advice!
Try varying your betta's diet a little. My bettas like the Bio-Gold too, but I also feed them Hikari freeze-dried bloodworms and daphnia. They like the pellets, but go crazy for the bloodworms!
Occassionally they get live brine shrimp as a treat -- brine shrimp should not be given more than once a week or two. But if your lfs
has the brine shrimp, try getting some to see if that will get your betta interested in eating again.