Planted Tank Obsessed
Join Date: Feb 2013
Location: West Palm Beach, FL
Bettas need to be in 78-80 degree water, preferably. Down to 76 is OK, as is up to 82, but it really isn't optimal for most bettas.
My tanks tend to run at or just below room temperature, with no heater. So, if it is 65 out, your tank will be too cold. Same problem can exist on the other side, if temperatures get too high.
The other issue is the daily temperature swing. More than a few degrees difference per day stresses the fish. This can wind up shortening their lifespan. In the wild, they can move around to modulate their temperature. Not so much in a small tank.
People definitely keep bettas in a huge variety of conditions. Some folks have great success far outside optimal parameters. I am kind of cautious when it comes to living things, so I would roll with just plants and snails.