Good to know the fish learned where he needed to go for air. Finding a heater and a filter for a tank like that would be rather difficult. I've never had a tank like that, so I don't think I can be of much help. Maybe a horizontally placed submersible heater like the Aqueon Pro 50w. Maybe place it underneath the tall part. Normally I recommend sponge filters for betta tanks, but I don't think it would work in your case. Unless the tank is more than 5 gallons and you plan to cycle it, you don't really need a filter. But I can understand why you would want one for water circulation.