Your best bet, aside from a generator, would be to use powerheads like Tunze or Vortech that have battery backup shoudl power go out. The biggest killer is stagnant water. My Tunzes can last for 30 hours with no power, and I could add more to that but it is such a rare occurance here(never more than 5 hours in 12 years) that its not worht it. Any more than 48 hours, it would be generator time since heating and lighting would start to need to be addressed. Battery operated air pumps are also an option for samller tanks.