I have a house that gets pretty cool at night in the winter and my pH
fluctuated quite a bit in my tanks until I put the sugar/yeast bottles in
heated water. I use cheap plastic waste baskets and the cheapest heaters I can
get that are vaguely reliable. As the pH of my tap water is 8.4, I use pretty
warm water for the bottles to get the CO2 levels high enough to get my tanks
down to 7.5. Please note, if you do this, you'll need to top off the water in
the containers pretty often as it evaporates faster than the tank water will.
Hope this helps.