When the power fails, years of work can be quickly ruined. And with extended outages, we are faced with a serious threat to the health of the fish. Here are a few things you can do if the outage exceeds one hour.
If the temperature of the room and the fish tank are vastly different, action needs to be taken to avoid heat loss/gain of the water. A small tank requires faster action because heat loss will be greater then that of a larger aquarium due to a smaller volume of water.
Use blankets or styrofoam insulation (if available) to "wrap" your aquarium in order to slow temperature loss.
Risk of overheating can be avoided by putting ice cubes in sealed plastic bags and placing them inside in the aquarium.
Once the power is restored make sure to slowly adjust the temperature back to normal as extreme changes can cause 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.
To increase oxygen levels use a cup to extract water from the tank and then pour it back into the aquarium. Repeat several times making sure an adequate 'splash' is created, assuring good oxygenation. Continue 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.
Remove the biowheels (if available) and submerge them in the tank to assure the beneficial bacteria do not dry out. 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.
After you're back up and running watch for signs of fish illness. Many parasites and bacteria are already present in the water and can attack a weak fish at any time. A prolonged power outage is extremely stressful for fish and the chance for disease greatly increases.
We recommend placing Algone in the filter during and after a power outage. Algone will control ammonia and hydrogen sulfite and help minimize their possible release into the water.
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.