Betta fish can have tropical flakes, but it can be a challenge to get them to eat them. They can be extremely picky eaters. Goldfish flakes are a bit different because they are designed for a completely different kind of fish. Goldfish are omnivores, so their food includes a variety of vegetable and protein bases. Bettas are carnivores (or more accurately, insectivores), so feeding them goldfish food may keep them alive, but it provides them with only a few of the things that they do need, and a lot of stuff that they don't. It is much easier to feed them a small-size pellet as a staple food, and bloodworms as a supplement. Adding a portion of cooked, deshelled pea once per week or so keeps their digestive system moving properly. Brine shrimp are a good treat, but have little to no nutritional value. It sounds like a lot, but in reality they should be fed only a small portion of food once per day, omitting one day out of the week.