A couple yrs ago I lost most of my fish due to power outage. I've since made changes to keep that from ever happening again.
I have a 12v deep cycle car battery hooked to a battery charger that is always charging and is designed to constantly run with load (Samlex 1215A). Then I have an inverter hooked up to the battery, with my main pump (and backup heater) plugged into it. So my main circulation pump is always running that way.
If power goes out, the battery takes over instantly. Been running with this setup for 3 years now. Last year I actually had it run my main pump for 18 hours with no problem.
Before this setup, I tried using various computer UPS backups. Started with the cheaper ones, which didn't work very well. Even tried some top of the line ones that I got from work (true sine wave ones), but even those only ran for a couple hours max. Eventually I'd love to get one of the whole house backup generators.....but don't have the $$ at the moment.
If anyone else is interested, I'd be glad to provide details on all the equipment. Setup seems to work pretty good for me and wasn't too expensive.
Also if anyone has one of those whole house generators, I'd really like to check it out and get more info.