Think of an aquarium as an intensive care unit, and the filtration system as the life support for your fish.
Sometimes we are not aware about the things we do that require power. It's not uncommon during a power outage, that we find ourselves trying to use electrical equipment, ending up in slapping ourselves thinking "Oh yeah, no power".
Aquariums are treasures, not only the sometimes high values but also the time and care you spent to make it look and work right.
Years of work, pleasures, and some hassles can be ruined by a power outage. There are a few important aspects we have to focus on when the power fails at rates exceeding 1 hour.
Fish are cold-blooded animals. We have to provide them with the water temperature best suited for them, either through a heater or a chiller.
Glass is a bad insulator, which means the tank will quickly adapt to the room temperature when our heater fails due to a power outage.
In order to keep the temperature as stable as possible blankets or Styrofoam come in handy. You can actually "wrap your aquarium with blankets or Styrofoam in order to slow the temperature loss.
The risk of overheating can be avoided by placing ice cubes in a sealed plastic bag in the aquarium.
Once the power is restored make sure to slowly adjust the temperature back to normal as extreme changes can cause extreme stress for your fish.
Oxygen levels in your aquarium will decrease with the increase in water temperature. Oxygen enters the water through a gas exchange at the water surface. If you think about blowing air into the plastic tube connected to your air pump, the effects will be very limited. The air stone actually provides little to no oxygen.
To increase oxygen levels you should extract some water with a cup and pour it back in the tank. This should be repeated at least once per hour, or as soon as you notice your fish gasp for air.
Lower tank temperatures will not only hold more oxygen, but also slow down the fish's metabolism.
The most important part of concern during a power outage is the filtration system. Remove the biowheels and submerge them in the tank. Filter media in trickle filters can be placed in a mesh bag and placed in the tank as well, or you can pour water over the media in regular hourly intervals.
Canister and other closed filters should be disconnected. These filters turn anaerobe rather quickly, producing highly toxic substances, which are deadly for the fish. One of these substances is hydrogen sulfite which smells like rotten eggs, the other ammonia. All filters should be cleaned, before they are restarted.
Other Things to Consider
Do not feed your fish during a power outage. Fish can survive 3-5 days without food. If you have to feed, do it sparingly. When the power comes back on, siphon the gravel, replace the carbon and do a 20% water change.
Another important part is to watch out for diseases. Many parasites and bacteria are already in the water and can attack a weak fish at any time. A power outage is extremely stressful and the chance for diseases to take foot hold are very high.
We recommend placing Algone in the filter during and after a power outage. Algone will control ammonia, and hydrogen sulfite in the filter and help minimize the possible release into the aquarium.
A power back-up system in the form of a car or boat battery will provide energy for at least one filter. Considering expensive fish, corals, live rock and other animals, this relatively small investment may be worth it.