Flagtails do live in groups in the wild. In fact, they do seasonal mass migrations related to reproduction. In an aquarium, large tank or pond nobody can replicate possibility of migration. Most people keep flag tails in tanks as solo fish in the long term, occasionally in groups or pairs in the short to midterm. A solo fish will do just fine in a tank with proper aquarium size, substratum, water quality, and feeding regime (they are quite adaptable). In such conditions they can live for decades and thrive, browsing their way and thus maintaining a tank very clean all along.
Good luck!
Good luck!
