Bettas need at least a 5-gallon with a filter and heater with it being around 70-80 degrees. Just letting you know and if that's a betta next to it I'd just move them apart or put something in between the tanks because all it'll do is stress them out seeing each other. I have a 7-year-old female betta in a 20-gallon with guppies and ghost shrimp as well as 2 dwarf otocinclus. :)