White Tetra Fish?

First, you should know that they shouldn't be in a tank with Goldfish, as Goldfish are coldwater fish, while Bettas and White Tetras are tropical fish. These fish (the Tetras) are mainly carnivores, though they will eat small amounts of vegetable matter, so I would strongly recommend a diet mainly of flakes and pellets with the occasional frozen bloodworm or brine shrimp meal (a few times a week). All the vitamins they need will be in the foods I listed above.