i have to agree with the previous posts, a 1 gallon jar isnt ideal for a betta,a 2.5 would be much better. a heater is needed if you dont live in a warm country and in a 1gallon jar, waterchange would have to be done every 2 days,where as in a 2.5 filtered tank, once a week.but its up to you what you do, no one can stop you.