... If long term power outages are this frequent, think about a small backup generator and a midsized UPS for the fish tank. Can get a self contained 1500va UPS for about 150. then a small generator for 300 or so, and have powerless runtime measurable in days, not hours.
That's the route I'm going.
My backup solution includes:
2 x APC UPS 1500 (net connected so I get emails/sms on power loss/restore) - should give me few hours to get the generator going.
12V Deep Cycle Battery to power the Tunze's via its failover kit - will keep the waterflow going if the generator is not hooked up for many more hours.
3000W Honda Inverter Generator (that will also run few other things at home) - when power is not back fast enough.