On Jun 19, 8:59?pm, Steven Schneider
wrote:

It's ~22 C (~72 F) on cool/cold days. This being summer, in a south
facing apartment, even in Canada it's often 27 C (80 F) or better.
I keep the water level lower so the output from the filter can
splash onto the surface, and we have fan that runs when the room is
in use.


72*f is a bit too cold for Bettas and Cories.
If you're water temp usually hangs around 80*f, that's fine.
However, if it's fluxuating back and forth, depending on the weather,
you may want to get a heater.
That way the temp will be steady. That's pretty important, as
fluxuating temps can really stress a fish.
The thermostat in the heater will turn it off when it's not needed and
back on when it does.