Aquarium Power Outage: Keep Your Fish Safe

You’ve done everything you can to ensure your fish have a happy and healthy environment. Their aquarium is a well-established living space outfitted with all the appropriate pumps, filters, heaters and lights necessary to provide an optimal ecosystem — but what happens when the power goes out? Here’s what you need to know about keeping your fish safe in the event of a power outage.

Preparing your aquarium for a power outage

The best way to prep for a power outage is to have a solid backup power system in place. For your aquarium (and other important household items), consider having an uninterruptible power supply such as a generator on hand. You can purchase one of these through most office supply stores.
 
During a shorter power outage, you may be able to mitigate any aquarium issues by using a spare battery-operated air pump and keeping a good supply of batteries on hand. This will provide the necessary oxygen replacement and water movement in your tank until the power comes back.

What to do for your aquarium during a power outage

Important Safety Tip: To help keep the tank at a consistent temperature and to minimize ambient light, cover it with a blanket.

If your power goes out, complete the following steps to ensure that your fish remain safe:

1. Check out the aquarium and other powered devices to see if the power has gone out all over your house, or if it’s only in some areas and your aquarium is still running fine
2. If you have an uninterruptible power supply setup, ensure that it’s running properly and is supplying back-up power to your aquarium
3. If you have a battery-operated air pump, place it in your tank, ensure that the batteries are new, and start it running (keep backup batteries nearby)
4. If you’re using a battery-operated pump and your power is out for longer than five hours, complete a 25 percent water change to help keep water quality safe
5. During the summer, you can float bags of ice cubes to add cool water and stabilize the temperature and oxygen content
6. In the winter, wrapping the tank with a blanket — taking care to avoid covering the top — can help to keep the water warm
7. Avoid feeding your fish when the power is out. Most fish — especially typical aquarium fish — can go multiple days without eating, and feeding during a power outage will increase the activity level of the fish, as well as their waste, which causes an accelerated loss of oxygen and a buildup of harmful ammonia and nitrites.

What happens to your aquarium and fish during a power outage?

You likely already know that power outages come in multiple forms and can last anywhere from less than a minute to hours or even days. The briefest of outages usually occur when a power grid is accidentally or temporarily shut down, your circuit breaker has issues or, in the most easily fixed case, the aquarium power cord somehow gets unplugged. Other outages caused by weather or natural disasters may take longer to get fixed.
 
An outage that lasts three hours or more could become problematic for your aquarium. This is because most modern aquariums use electricity to run all of the essential parts that keep it stable, like those pumps, filters, heaters and lights mentioned before. Without electricity to keep all of those moving parts functioning, the environment in your pet’s aquarium become unsettled very quickly. Without power, the most common issues to occur in an aquarium include:

1. Oxygen depletion. Your fish will still consume oxygen in the aquarium, even if that oxygen isn’t being replaced with the help of your filter. As the aquatic life in your tank slowly uses up what’s left, a dangerous oxygen depletion will start to occur.
2. Water temperature variation. Most aquatic species need water temperatures of 72 to 82 degrees Fahrenheit to remain healthy. Changes in water temperature may stress your fish, which then puts them at risk for disease. Additionally, as temperatures rise in the aquarium, water begins to lose its capacity to hold oxygen.
3. Ammonia buildup. Without a working filtration system, the ammonia in your aquarium could reach levels that are toxic to your pets.

Caring for your saltwater aquarium during a power outage

If you have a saltwater tank, you’ll want to ensure that many of the same systems are accounted for, including maintaining oxygen levels and keeping a system of moving water. Most saltwater fish can last for days without light, but maintaining oxygen levels is important. Without the help of an uninterruptible power supply, you can manually help supply oxygen to the tank and keep water moving by filling a cup or pitcher with tank water and pouring it back into the tank. Doing this — for a few minutes at a time every 10 to15 minutes — helps add oxygen to the water as well as circulate it through the tank.
 
A little preparation and forethought can go a long way to ensuring that your aquarium remains in a stable condition and continues to provide your fish with everything they need to ride out the outage. 

Frequently Asked Questions

How long can fish survive without power? Most typical aquarium fish can tolerate a power outage of up to three hours with minimal risk. Beyond that point, oxygen depletion, temperature swings and ammonia buildup begin to threaten their health. Outages lasting more than five hours require immediate intervention — a battery-operated air pump, a partial water change and temperature management. Saltwater tanks and tanks with sensitive or delicate species may show stress sooner, so monitor your fish closely from the moment power is lost.

What water temperature do aquarium fish need, and how quickly does it change during an outage? Most freshwater aquarium fish need water temperatures between 72°F and 82°F to stay comfortable and resist disease. Water temperature can begin dropping (in winter) or climbing (in summer) within the first hour of an outage, depending on your home's ambient temperature. As water warms above that range, it also loses its capacity to hold dissolved oxygen — compounding the danger. Covering the fish tank with a blanket helps slow temperature drift in either direction. Merck Veterinary Manual

Should I feed my fish during a power outage? No — skip feedings for the duration of the outage. Most aquarium fish can go several days without food without harm. Feeding during an outage raises fish activity levels and increases waste, which accelerates oxygen consumption and causes ammonia and nitrite to build up faster in a tank that has no working filtration to process them. Resume normal feeding only after power is fully restored and your filter has been running for at least a few hours.

When should I do a water change after a power outage? If you are relying on a battery-operated air pump and the outage extends beyond five hours, perform a 25% water change to dilute accumulating ammonia and nitrites and help stabilize water quality. After power is fully restored, monitor your water parameters closely for 24–48 hours and consider an additional partial water change if ammonia or nitrite readings remain elevated. If you don't have a test kit on hand, consult your veterinarian or an aquatic specialist about next steps. Merck Veterinary Manual

Is a saltwater tank more vulnerable during a power outage than a freshwater tank? Saltwater (reef and fish-only) tanks are generally more sensitive because the corals, invertebrates and many marine fish species have narrower tolerances for oxygen fluctuation, temperature change and water movement. Most saltwater fish can survive several days without light, but oxygen and circulation must be maintained. If you don't have a backup power supply, manually pour tank water from a cup or pitcher back into the fish tank every 10–15 minutes to add oxygen and keep water circulating.

What signs of stress should I watch for in my fish during or after an outage? Watch for gasping at the water's surface (a key sign of low oxygen), erratic swimming, clamped fins, loss of color or unusual lethargy. These can indicate oxygen depletion, temperature shock or ammonia toxicity. If fish show persistent distress after power is restored and water conditions have been corrected, contact your veterinarian — particularly one with aquatic experience — for guidance. Merck Veterinary Manual

Power Outage Risk by Duration: Quick Reference

Backup Power Options for Your Fish Tank: At a Glance

Choosing the right backup solution depends on your tank size, budget and how long outages typically last in your area. Use this table to compare your options before an emergency strikes.

Petco tip: For most freshwater fish parents, a battery-operated air pump paired with a modest UPS covers the majority of outages. If you share a life with a saltwater or reef tank, a portable power station is worth the investment — the livestock in those systems is far more sensitive to oxygen and temperature swings. Changes in water temperature can stress fish and put them at risk for disease, so maintaining stable conditions is a priority during any outage.

Frequently Asked Questions

How long can aquarium fish survive without power? Most common freshwater fish can tolerate a power outage of up to three hours with minimal risk, but outages lasting longer begin to deplete oxygen and allow ammonia to build up to levels that can be harmful. Saltwater and reef species are generally more sensitive. Consult your veterinarian or an aquatic specialist if you are unsure about your specific fish.

Should I feed my fish during a power outage? No. Avoid feeding your fish while the power is out. Most aquarium fish can go several days without food, and feeding during an outage increases their activity level and waste output — which accelerates oxygen loss and causes ammonia and nitrite to build up more quickly.

How do I keep my fish tank warm when the power is out in winter? Wrap the sides and back of the tank with a blanket or towels to slow heat loss, taking care not to cover the water's surface so gas exchange can still occur. A UPS or portable power station running your heater is the most reliable solution for extended cold-weather outages.

How do I cool my fish tank during a summer power outage? Float sealed bags of ice cubes in the tank to gradually bring the temperature down. Add them in small amounts and monitor the water temperature closely — a sudden drop can stress fish just as much as overheating can. Most aquarium fish need water temperatures between 72 and 82 degrees Fahrenheit to remain comfortable.

When should I do a water change during a power outage? If you are relying on a battery-operated air pump and the outage extends beyond five hours, perform a 25 percent water change to help dilute ammonia and nitrite buildup and support water quality until full filtration is restored.

Is a saltwater tank harder to manage during a power outage than a freshwater tank? Yes, generally. Saltwater and reef systems depend on stable oxygen levels, water movement and, for reef tanks, lighting — making them more vulnerable during extended outages. Manual aeration (filling a cup with tank water and pouring it back in for a few minutes every 10 to 15 minutes) can help in a pinch, but a reliable backup power source is strongly recommended for any saltwater setup.

This article was created with assistance from AI tools and reviewed for accuracy by Petco's content team.