Clean the filters now. Was filter media in a bucket of tank water and re-use the media. Then if there is a power failure, there will be less gunk in the filter using the oxygen.
During a power failure.
If you have external canister filters, you can take the outlet hose and put it in a bucket next to the filter. Allow the bucket to fill with water and then put the outlet hose back in the aquarium. Pour the bucket of water back in the tank. Do this every few hours and the filter will be fine. Alternatively, take the filter media out of the filter and put it in the tank. Then aerate the tank water with a battery air pump or by blowing air through airline into the water.
With HOB (hang on back) style filters like the AquaClear, just get a bucket of water from the tank and pour it in the filter. Do this every few hours. Again you can take the filter media out and put it in the tank but that's not as necessary as it is for canister filters that are sealed up.
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Insulate the back front and sides of the tank to help trap heat.
Make sure your gas heater is flued because the gas fumes are toxic to people, animals and fish (carbon monoxide poisoning).
Don't feed the fish during a power failure. They can go a week without food.