As the title states... is a 2.5 gallon tank with a heater, thermometer, and a live plant, too small for a single betta? I use a gravel siphon to remove water and do changes twice a week (50-75% and then 100%) I also check the ammonia levels with the API liquid test kit on a regular basis. I have successfully kept Jacob alive and happy with this routine for months but now I am doubting myself... Someone told me the minimum was five gallons but... I don't really have room for two five gallons... I was really hoping to keep all my boys in a minimum of 2.5 gallons so I could afford to get a 20 gal for either a sorority or tropical community. But if I need to upgrade everyone then so be it. I will do what's best for the fish. I just hope I'm not hurting two of my boys by keeping them in under five gallons.