personaly i like to give all my bettas 5 gallons each. lots of plants and decor and enough room to move. but i suppose a 5 gallon could be devided, even tho i would never do it. that only gives the betta 2.5gallon. the least i would go is 3 gallon. but a 10 gallon devided is the ideal set-up for me.no less than 2.5/3 gallons per betta tho