He should be getting a blood worm a week in replace of pellet meal as a treat. He should also be getting one fast day a week.
I would find another pellet.. those are one of the worst on the market, sorry. The pellets should have the first or three ingredients as whole
fish, not fish meal or even worse is wheat. That pellet is almost entirely wheat, corn, potato and soybeans. They should also have limited unnatural additives like preservatives and food coloring - though vitamin additives are good. It doesn't surprise me that he didn't like them to begin with.
PetCo sells New Life Spectrum Betta (feed 5-8 split up into 2-3 feedings + fast day) - may be with other NLS foods or the betta section, depending on how your store is set up. We actually have 3 sections in mine I have to look in when i go :S Otherwise Omega One Betta Buffet is a good one - feed 3-4 split up into twice feedings and a fast day a week. Omega One may be found at Petsmart.