Betta Fish: improvements to temp tank?

rescued this betta recently and only had a cycled 2.5gal available. the plan is to upgrade to a 5+ in january after i go through a move. however, what can i do in the mean time to make this better for him? heated to 80, filtered, 25% water changes 3x a week and daily testing. he’s already improved drastically in a week, so much more life and recovered from his ammonia burns! also, the algae is a WIP… the tank was a feral planted mess for nearly a year.