Originally Posted by bettafish15
20% a week is on the small side, you should change out 40-50% a week because you'll be cycling for a month. Maybe after your tank is mature you could do 20% a week, but that wont be for awhile.
This is true. I was assuming you'd do a fishless cycle but with a fish in you'll want to change 40% weekly until your tank grows enough bacteria.
Also, once your tank has been running for a while and has cycled, if you were to have a 10 gallon you could put a plastic divider in and keep 2 bettas in there-- they'd each have 5 gallons. It's just a suggestion. :) Good luck with your 10g!