Removal of waste produced by the fish will become a serious priority with loss of power. In the first 24 to 36 hours after a power loss, the fish should not be fed at all, and only very, very lightly after that. Daily cleanings of waste from the substrate, with small amounts of water changed out, will insure levels of toxic Ammonia and Nitrite produced in the water remain manageable by your improvised, battery powered, sponge filtration. If you are on a water well system or live in an area that routinely loses water pressure with loss of electricity, you should give serious consideration to providing a ready source of pre-treated/conditioned water for your fish. This can be easily accomplished by the use of a water-filled plastic trash can, situated nearby the aquarium.
When the power does go off, and it seems likely that it will be for a longer duration than a few hours, then you must rig the aquarium for operation without power filtration.
1) Remove the glass tops. Doing this will insure proper aeration of the water within the tank for the fish, and enable easier access to the interior of the tank for performance of frequent cleanings or adjustments to improvised filtration equipment.
2) Unplug all electrical equipment connected to the aquarium. Periodic fits and starts of the electrical power to the aquarium will merely insure the destruction of un-primed power filtration or dangerous variations in temperature within.
3) Rig up your improvised, battery powered sponge filters and get those things running! Placing the top of the plastic tubes no more than an inch or so from the surface of the water will decrease water pressure on the air stone and insure vigorous bubbling and water current through the sponge pre-filter. The colony of beneficial filtration bacteria may be low in numbers initially on these sponges, but will grow out at a fast rate. The sooner they are started, the better they will work and the faster the tank will be replenished with oxygen.
4) Open up all canister filters to expose the water and media inside, to at least a bit of air and oxygen. Carefully rinse out all the canister media in de-chlorinated water, then return to the open canister media container. This will prevent the die off of all the beneficial bacteria colonized on the canister media and will help to establish biological filtration much faster in the aquarium once the electrical power returns. Remove and carefully rinse in de-chlorinated water all sponge filters and filter screens from Hang-On-Back power filters and simply place inside the aquarium. Much of the beneficial bacteria established on these filters will survive by doing this as well.
5) The last part will be insuring the water temperature remains stable and does not go too high, or too low. If in summer, the windows of the house must be opened to permit a bit of a cooling breeze to insure the water within the tank does not become too warm. Prevent direct sunlight from entering and heating the house by closing shades or curtains. In winter, it gets tougher. A kerosene burning heater will keep the air temperature within the house to a warm level. Keeping this kerosene space heater burning may be all you have available to keep the water warm enough for your tropical fish to survive. In the interim, heating water on a gas burning stove will provide a source of heat for the aquarium, but be careful! Heating the water directly like this is extremely dangerous, as water may be heated too fast causing a wide variation in temperature within the aquarium and a LOT of killing stress on your fish. When power does return, be careful to heat up the aquarium very slowly. Heating things back up inside an aquarium too fast after very low temperatures have been experienced, will almost certainly kill your fish. A terrible thing to happen in the end, after you've worked so hard to save them!
A loss of power can be very troublesome and annoying to say the least. But, with preparation, ingenuity and a bit of extra work, this will not necessarily mean certain disaster for your fish. In the fall of 2003, during the aftermath of Hurricane Isabel, I experienced 11 continuous days of NO electrical power, and NO running water!. By performing these emergency techniques on eight aquariums, containing a total of over 70 fish - I didn't experience the loss of a single fish! Good Luck with it, don't despair and most important - don't give up on your fish! □