Just thought I would share my personal experience with power outage and UGF filters.
We had a bad wind storm 1 1/2 years ago, that knocked our power out for 5 days. At the time, I had 5 tanks running, most evenly stocked. My 65 gal tank with ugf, nitrites and ammonia, where much harder to keep under control.
Luckily, the power was out most everywhere, so no school or work. This freed me up to do 2 pwc a day on all my tanks to help oxygenate the tanks for both the fish and bacteria. So, without a generator available, the water changes and battery air pumps, kept my fish alive. On day 2, I was getting ammonia and nitrite readings on all of my tanks, the 65 gal with ugf, the levels where much higher and more water (with gravel cleanings) had to be changed out, to keep the levels "safe".
I have since removed my UGF.
Just in case you where wondering, no mini cycles. The power was returned on a Thursday night, Friday morning, all tanks tested zero for ammonia and nitrite.