Only place one betta in a 10-gallon tank. Male bettas cannot live together due to their aggressive nature. Likewise, a 10-gallon tank is too small for a female betta sorority. Betta sororities need at least a 20-gallon tank. A larger tank prevents territorial behavior among the female bettas. But a 10-gallon tank is suitable for adding small tank mates with your betta. A general rule of thumb is 1" inch of fish per 1 gallon of water. The best tank mates for a 10-gallon betta tank include: - Mystery snails - Ghost shrimp - Amano shrimp - Otocinclus - Plecostomus Do not overcrowd your betta tank, and watch for aggressive behavior.