Bettas prefer not to be placed into a tank with other fish and do best when they swim alone. These fish are not schooling fish, so they will fight other bettas when placed in a tank together, according to Pet Sitters International.
When setting up a tank for bettas, choose a bowl that can hold at least two gallons of water. Add dense plants and aquatic caves to give the betta a place to hide and to make the fish feel safe. The water in the tank should be changed regularly and maintained at a temperature between 76 and 82 degrees Fahrenheit. Water that is kept too cold can cause illness.