How Long Will Fish Survive In A Tank Without Power?

by Aquarium Scoop | Last Updated: November 29, 2022

Power outages are a scary event for both aquarium owners and fish. Loss of power creates unstable water temperatures and lower oxygen levels.

In this guide, you’ll learn:

  • How long can fish go without power?
  • How does a power outage affect your fish?
  • How can you prepare for a power outage?
  • What to do during a power outage

Several consequences of a power outage on fish include stress, loss of appetite, and decreased immunity. Therefore, if your fish tank loses power, it’s essential to take immediate action to ensure the safety of your fish.

How Long Can Fish Go Without Power?

Fish can go without power for 6-12 hours. Longer than that, oxygen levels can become dangerously low. The more crowded your tank, the shorter your tank will last.

Here’s what you need to know to keep your fish safe during a power outage:

If the power outage is prolonged, fish may die from a lack of oxygen or ammonia build-up in their tank.

Once the power comes back on, give them small amounts of food until they adjust to their regular feeding schedule.

Expert Tip 🧠

If you have an HOB filter, regularly pour tank water over it to promote circulation to your bacteria.

📚 Read More >> How Much Electricity Does A Fish Tank Use?

What Are the Consequences of a Power Outage on Fish?

If the power goes out, your fish will be just fine – as long as it’s not for an extended period. Many aquarium owners have gone days and even up to a week successfully keeping their fish alive.

First and foremost, when the power is out, so is your filtration system. This means oxygen levels will start to drop, and water quality will decline quickly.

This isn’t ideal for your fish, who rely on clean water to stay healthy. In addition, all that extra waste in the tank can lead to ammonia poisoning, which is incredibly dangerous (and often fatal) for fish.

To help combat these issues during a power outage:

  1. If possible, move your fish into a smaller temporary tank with an air stone or bubbler running off battery power – this will help maintain dissolved oxygen levels in the water.
  2. Do frequent partial water changes using fresh dechlorinated water.
  3. Keep an eye on ammonia levels using test strips (if they rise too high, you’ll need to do a larger partial water change).
  4. Be prepared with food and medications ahead of time if your fish get sick from the stress of being moved or from poor water conditions.

While a power outage won’t necessarily kill your fish outright, it can cause some severe stress and health problems if not handled properly.

By being prepared and taking action quickly, you can minimize the risks to your fish during a power outage.

How Can You Prepare Your Fish for a Power Outage?

1. Fill Up a Clean Tub With Cool Tap Water and Place All of Your Fish Inside of It.

This way, they will have plenty of oxygenated water until the power comes back.

  1. If possible, move your aquarium into a more temperate room so that the change in temperature doesn’t shock your fish.
  2. Keep an eye on the clock and check on your fish every few hours to ensure they’re still doing okay without any aeration or filtration in their temporary home(s).
  3. Be prepared with food and feed only what is necessary so as not overfeed them while they’re confined to pooled waters; uneaten foods could pollute these waters very quickly and endanger everyone’s health therein – including yours!
  4. When the power finally returns… return each fish carefully back into their regularly scheduled lives within their appropriate habitats.

Use a backup battery to be prepared for power outages


How do you keep fish alive during a power outage?

Without power, fish cannot survive for more than a few hours. This is because they rely on aeration from the filter to oxygenate the water. Without this circulation, the water will quickly become stagnant and suffocate the fish. In addition, the tank heater will no longer work without power, causing the water temperature to drop, which can also kill your fish.

What happens to fish tank if power goes out?

If the power goes out, the fish tank will eventually become too warm or too cold for the fish to survive. If the power is out for a long time, the oxygen in the water will start to deplete, and the fish will suffocate.

How long can fish survive without air pump?

Fish can survive for a short period of time without an air pump, but eventually, they will need one to aerate the water and prevent them from suffocating. Without power, fish can only survive in a tank for a few hours at most.

How do you oxygenate water for a fish power outage?

You need to make sure that you have a way to oxygenate the water for your fish. One way to do this is by using an air pump with an airstone. Another way is to use a battery-operated aerator. You can also use a generator to power an air pump.


A power outage can devastate your fish tank and the creatures inside it. Without power, filtration systems will cease functioning, and oxygen levels will quickly drop.

This can cause severe harm or even death to your fish. To avoid this, it’s important to have a backup plan in place for when the power goes out.

Aquarium Scoop is dedicated to providing the best care for your fish and other aquatic life. We offer various services to help you keep your aquarium in top condition, including educational resources on taking care of your fish and other aquatic life.