The tanks are insulated and in theory the attic shouldn’t get *that* cold, and being they’re gas I’d throw them into vacation mode or drop the temp after shutting off water to the house. My uninsulated 60 gallon fish tank was fine for 24-36 hours without power during a really bad winter storm once, it only lost ~10F, the (poorly insulated) house dropped almost 30.My main question is what to do with the darn water tanks?