Welcome to the forum! i noticed your "tank" is REALLY small....a betta should have at least 2 gallons to itself, preferably with a heater AND filter. Heaters ar needed for Betta because they come from Thailand, where their water has to be at a constant 80 degrees or they get lethargic and their bodily systems become weak. 5 gallons is the bare minimum IMO to divide if you would like a healthy and happy fish. Just because a fish could "survive" in a small "tank" dosent mean it will "thrive" and be happy. Please remember, it is like a person living in a closet for it whole life.
Please research and don't make your bettas suffer!!!
-a concerned viewer
Sorry if i came off as rude, i busted wanted to get my point across :)
You can PM (private message) me if you have any questions at all, and i can answer them or at least point you in the right direction :)