I use Hikari Betta Bio Gold. They are small and easy to use. My bettas eat them as soon as I put them in the water so there isn't any left over food to decay and cause problems. I feed 3 in the morning and 3 at night. You might want to also get some brine shrimp or blood worms for a treat occasionally. If you only have the one fish, I would suggest freeze dried or maybe frozen (cut the cubes into pieces or just scrape some off into the tank). Be careful not to use these too much though as brine shrimp are not very high in nutritional value, thus kind of like use eating a snack. Blood worms on the other hand, are very high in protein so they are difficult for them to digest and can cause constipation problems.