i have my betta in a 2gallon setup with an african dwarf frog. just make sure to have lots of hiding spots because the betta seems to hunt the frog if theres not. the frog hides in the little rock cave on the bottom or in some of the plants. its a nice little setup, only thing is because there is 2 fish in a small environment, the water gets dirty fast and i have to do water changes every 2-3 days. my setup is not heated, but stays around 78-80 degrees because its kept on a dorm room desk. I would have loved to go bigger, but could not due to space restrictions and budget.