Power failures any time of the year present a risk for your fish. If you live where it gets very cold, a power failure can prove lethal for your aquarium fish. Here are ways to prepare for, and deal with the worst-case scenario - a power failure in the dead of winter.

Maintenance In Cold Weather
A tank in tiptop shape will fare much better during a power outage. Keep the tank well vacuumed, clean the filter media regularly, and perform frequent water changes.

If you use an air pump, make sure it is fitted with a check valve so it won't siphon water during a power outage. Keep a thermometer on or in the tank so you can monitor the temperature during a power failure.

Prepare an emergency kit and keep it near the aquarium so you don't have to search for it in the dark. If you are going to be away from your home for an extended period of time, make arrangements for a neighbor to tend your fish during a power outage.
The Emergency Kit
First and foremost be prepared to move around in your home. You can't do much for your fish if you are groping around in the dark. Have a flashlight nearby with fresh batteries in it. In addition to your flashlight, prepare a simple emergency kit for your aquarium. There are only a few items you need, but they could make all the difference in the world for your fish. Here is what you'll need:
 

• Flashlight with fresh batteries
• Pencil and paper
• Blankets or thick towels
• Rope or sturdy tape
• Small plastic container with lid or zip lock bag

• Battery operated aerator and batteries
• 1 to 2 cup plastic container with a pour spout
• Hand warmers
• Fish net
  (A copy of this article would be helpful too)
   
  

During a Power Failure
If the power goes out, your aquarium will lose three important elements: heat, air (from lack of water movement), and filtration. Initially the tank is not in immediate danger. However, if the power is not back in twenty to thirty minutes, assume the worst and take steps accordingly.

Maintain Heat
Jot down the initial water temperature, so you have a yardstick to go by. Fill the plastic container or zip lock bag with hot tap water, then seal it and place it in the aquarium. Even though your water heater no longer has power, the water will still be warm enough at this point to be of benefit.

To retain as much of the heat as possible, wrap the tank with thick towels or heavy blankets. Use rope or sturdy tape to secure them as closely as you can against all sides of the tank. Lay at least one blanket over the top of the tank.

Aerate Water
Place a battery-operated aerator in the tank to keep the water moving while the filter is off. You can purchase aerators at a pet shop or even a bait shop. If you have more than one tank, rotate the aerator for ten minutes at a time in each tank. If you do not have an aerator, and the power is out for more than an hour, you'll have to hand aerate the water. Use the small plastic container to remove a cup or two of water, then hold it well above the water level and pour it back in (the idea is to agitate the surface of the water when doing this). Repeat this process for five minutes out of each hour.

Now all you can do is wait for the power to come back on. Do not feed the fish during the outage. It will cause them to produce more waste, which cannot be eliminated readily without the filter running. If the power is out more than two hours, remove the filter media from the filter unit. Otherwise it will pollute the tank with dead bacteria when the power comes back on.

Monitor the water temperature, and continue aerating the tank. In the event a fish dies suddenly, remove the body immediately so it does not impact the biology of the tank. As the temperature continues to fall, remove the container holding hot water and refresh it with hot tap water. The water in your insulated water heater will stay hot for many hours. If your tap water is no longer hot, seal a hand-warming unit in the container and place it in the tank.

When the Power Comes Back
Check the temperature of the tanks. Adjust the heater so the temperature slowly rises at the rate of a half a degree every couple of hours (the idea is to slowly adjust the fish to the return to normal temperature). If the filter has not been running for more than two hours, replace the filter media with fresh media. Do not feed the fish immediately. Wait until the water temperature has returned to normal. After 24-48 hours, test the water for ammonia and perform a water change if any ammonia is detected. A week later test the water again to be sure that everything is back to normal.