i have 3 bettas.one is in a quite large tank with heater,live plants the works!happy as larry made a bubble nest almost immediately.the other two are in smaller tanks with a fake plant each but no heater.when i change water i fill half there tanks with water from the main and the other half with conditioned room temp water.the problem is their tank water is getting too cold.its definetly not anywhere near 70 F.small heaters are hard to get.any ideas?