Harlequin Rasbora, Tetra fish like Neon Tetras, Glowlight Tetras, Ember, and Cardinal Tetras, makes great Betta fish tank mates because of their speed. Even if betta shows a little aggression, these fish will be able to outswim betta every single time. Other best betta tank mates are Mystery Snails, Cory Catfish, Ghost Shrimps, Clown Plecos, Otocinclus Catfish, and Kuhli Loaches because they’ll never get in each other’s way, some of them will clean your betta tank, and they require same water parameter as betta needs.