I'm kinda anal about backup power. Being a ham radio operator and an emergency communications buff I've been doing this a long while. All my ham gear is powered by photovoltaic panels and a large battery bank. Unfortunately, the ham gear and solar power system is too far from the aquarium room.
So, in the fish room (actually the dining room) there are three tanks, two FW and one SW. I have a 12VDC RV/marine dep discharge battery and a 300 watt inverter under the main tank stand. There's also a battery charger to keep the big battery topped off. In the event of a power failure I flip the breaker for the dining room on the main breaker panel in the garage. That isolates all the plugs in the tank (dining) room from the mains. I then plug a double male ended extension cord from the inverter into one of the room sockets to backfeed 120VAC to all the sockets on the circuit and hence all the tanks. (Yes, I know, all the electricians and electrical inspectors are freaking out at this point. Know what you are doing before you try this.) I then turn off the unnecessary equipment in each tank setup, keeping circulation, filtration, and heat if necessary.
The battery will keep things going for several hours with some judicious load management. If it looks like it is going to be a longer outage, I fire up the 6500W generator and run a HD extension cord into the house. I again backfeed the fish room circuit, and also power up several other loads in the house (coffee maker, 'fridge, microwave) for creature comforts (mine!) One of these days I'll wire up a legit, code compliant transfer switch.
If that generator fails, there is another 2400W gasoline generator available to fall back on. Now it's just a matter of having to have enough gasoline around to feed the generators, and staggering the operations times to avoid a hot refuel.
When power returns, carefully reverse the process, remembering to pull the backfeed before resetting the breaker to restore power to the fish room. It's safe if you know and watch what you are doing. If not, see an electrician about a legit transfer switch.
