How Long Can Fish Live without Power?

Not long ago, I had a friend who had a scare in her house with a power outage. Although it only lasted for a few hours, she became concerned about the fish in her aquarium. She reached out in a panic and I did some quick research to find out how long fish can live without power, and ultimately came up with this quick guide as a result.

How long can fish live without power? Fish can live without power for approximately 2 days. However, this number could be larger or smaller, depending on the amount of fish in the aquarium, the size of the aquarium, how healthy the fish are, and a few other conditions we’ll discuss.

If you ever find yourself in a situation where you lose power, it is important to be proactive and have a plan for your fish. While it is true that the fish can survive for a period of a few days, this will only be possible if you take the appropriate action. They’re counting on you!

In this article, we will be going over the essentials needed for keeping your fish alive during a power outage. Keep reading to find out what you need to do in this situation and how long you have until something goes wrong.

What to Consider When You Lose Power?

If you own a fish tank or you’ve ever taken care of one, you’re likely familiar with the components that go into keeping one running. These components, of course, require the use of electricity.

So, in the event of a power outage, your fish tank will immediately be affected along with the components that go into keeping the tank’s water temperature at the correct level as well as keeping the water clean and oxygenated. Ultimately, you will need to have a source of power in order for your fish to survive.

Take a look at the list down below to find some of the factors that we will be considering in this section, in relation to why fish need the power to survive.

Why Fish Need Power to Survive:

  • Oxygen
  • Temperature
  • Filtration

Air pumps provide oxygen so the fish can breathe. However, water temperature plays a role in oxygen saturation — so, water heaters are installed to help regulate the water temperature. If the tank gets too hot then the oxygen levels will lower. In higher temperatures, your fish’s metabolism will also be higher, which will increase their need for more oxygen. Filtration systems ensure decaying matter, excess food, and other floating debris (fish waste) is removed from the water. Filtration systems also work to ensure the tank is free of bacteria and diseases.

That’s why the power to the fish tank is essential to ensure your fish are able to thrive and survive.

In the rest of this section, we will be answering the main question of how long fish can live without power and when should you begin to worry about your fish?

Factors To Consider:

  • The temperature of the water
  • How healthy the fish are
  • The last time they ate
  • How many fish are in the tank, and how much room they have

When the power source of your aquarium goes out, the temperature of the water will have a big effect on how long your fish are able to survive. They must always maintain a certain body temperature, which is directly linked to the water temperature. As it relates to tank temperatures, generally speaking:

  • Coldwater fish prefer temperatures below 68°F (20°C)
  • Tropical fish prefer temperatures between 75-80°F (24-27°C)

There are species that like specific temperatures a little higher or lower than the tropical fish range. So, you really need a reliable thermometer to keep an eye on the tank temperature. Give your local fish store a call and verify temperatures and keep those numbers on an index card in your pet’s emergency kit. You do have an emergency kit for your pet, right?

Additionally, their survival rate will depend on how healthy they are, the last time they ate, and how many other fish are in the tank. Ideally, your fish will have a lot of extra room to live and move around, giving them a slightly longer time frame for survival without power.

What Should I Do To My Fish Tank If I Lose Power?

So, now that you know all of the reasons why fish tanks need power for your fish to survive, as well as how many days you can expect your fish to live in the event of a power outage, this just leaves one question: what do you actually do for your fish tank if you end up losing power?

As soon as your power goes out, you need to jump into action to protect your fish. While it is true that the two-day mark is the overall average in these scenarios, you will need to do some work and take preventative measures to help them survive in prolonged outages.

To protect your fish follow the following steps:

  1. Try to control the oxygen by removing some water. Fish can actually live in a few inches of water and they will agitate the water by swimming around, which will introduce oxygen
  2. Monitor the temperature with a reliable thermometer
  3. Remove the filtration bio wheel so that toxins don’t build up. If you use canisters they should be disconnected
  4. Remove the plants and other substrates from the tank to keep decay from getting into the water
  5. Try to keep the tank at room temperature the best you can
  6. Do not feed them, the food will contaminate the clean water (they can live up to a week or more without food)
  7. Consider taking them to a family member’s home or friend’s home, if possible

Ideas on controlling temperatures and oxygen


Controlling water temperature may be a bit easier than you think. Both require a good thermometer, like this one, which should be monitored frequently when using these strategies.

Keep 85°F in mind. You really don’t want the water above that temperature.

Lowering water temperature can be done easily with ice. Just keep the ice contained in a ziplock bag or use a frozen bottle of water you’ve kept in the freezer for this purpose.

Raising water temperature can be done easily with the same water bottle concept. Just warm up some water on the grill, camping stove, or fire and pour into the bottle. Not too hot though. Safer to repeat this step a couple of times versus placing boiling water in the tank. If it’s too hot to touch, it’s too hot for the tank.

NOTE: I’ve read many articles that tell readers to pour ice cold or boiling water directly into the tank to either lower or raise the temperature. Please don’t do that. You have no way to control the temperature and you don’t want to shock the fish. Removing the bottle, whether it has ice or hot water, allows you to be in control. You don’t have that luxury when dumping water directly into the tank.

You can also wrap your tank with towels or spare clothing to help insulate the tank and maintain the water temperature. Grab any materials you can and tape them to all four sides. Consider partially covering the top of the tank to slow down how the temperature escapes.


We previously mentioned lowering the water level and letting the fish agitate the water themselves. If you’re not comfortable with this method there are some inexpensive failover pumps worth considering.

This popular model plugs into the wall but fails over to a battery when the power goes out. Very convenient and no disruption.

If you need to transport your fish or even leave your home, then you’ll want to consider a solar power oxygenator air pump as an alternative. This is a reasonably priced pump with the luxury of portability.

What else should you do or not do?

  • Do not feed the fish (or do so sparingly)
  • Consider placing Algone in the filter

In order to protect your fish in a power outage, you should refrain from feeding them as long as you possibly can. Fish can go up to a week without eating in general, so depending on the last time you fed them, you might be able to go without feeding during the entire power outage.

In the worst case scenario, feed them very sparingly. The last thing that you want to do is ruin your clean water in an emergency.

We’ve also read plenty of positive reviews from customers who are fans of placing Algone in the filter during and after power outages. Algone will control ammonia, and hydrogen sulfite in the filter and help minimize the possible release into the aquarium.

Can treat 330 gallons


In conclusion, if your power ever goes out, you won’t have to panic or worry too much about your fish not surviving. Remember, you’re a planner which is why you’re here. Put your plan together, create an emergency kit for your fish, and implement your plan when the power goes out.

Your fish will thank you for it!

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