Okay, so I just bought a little heater for my betta's jar. I've been reading about how often to change the water, and that it's important to let the water sit before re-introducing your betta into it, and it's also important that the new water be as close to the same temperature as the old water.
So, if the water in the tank is heated, how do you change the water without letting the betta sit in colder water for a while? Or putting colder water in the tank?
The water sitting will loose it's heat, regardless if it's the water the betta is waiting for a clean tank in, or if it's the water that will replace the water in the tank.