if you are down 8-12 hours.. get a generator, no question about it.
a lot of people will push inverters over a ups, well a cheap inverter is what is in the ups they are complaining about.
And frank, i was under that thought to, before a reg on club forum enlightened that indeed circulation is MUCHo necessary.
btw, a small powerhead pointing up, gets both of this oxygen by agitating surface and circulation.
personally using a 600w ups, and doesn't take long to deplete it with the return pump on it,
Working on a diy idea to use the ups to startup a generator.
Problem is making sure the generator is disconnected as soon as power is restored so that it doesn't get fried or fry something else. Auto transfer switches aren't cheap.