How To Keep My Fish Alive During A Power Outage

Every aspect that you purchase for your aquarium is important. They all have a specific duty in maintaining your aquarium and keeping your fish healthy and alive. The filtration system, the substrate, the tank heater, the lighting, and even the added decorations.

If all of these elements are not cared for and working properly then you are going to have polluted water and sick or dying fish. Most of the elements above have to be plugged into a power supply to do their job. So, what happens if your power goes out?

How do you keep your fish alive during a power outage? If the power outage lasts 3+ hours, the best thing to do is have some sort of battery back-up device hooked to your tank. This is plugged into the main power supply and when there is a power outage it will automatically convert to the battery supply. 

There are 2 types of battery-powered pumps that you can choose from. You can purchase a manual battery back-up, just add batteries and turn it on. Or you can opt for the electric battery back-up.

It is extremely important to have a battery back-up to keep the filter running during a power outage. This helps to keep the water flowing and agitated to offer oxygen to your fish. 

Today, I am going to cover the different ways to handle a power outage when you have an aquarium. We will discuss emergency power supplies, aquarium battery back-ups, and more. Unfortunately, you never know when a power outage is going to occur or how long it is going to last. Even a scheduled outage could last longer than intended or expected.

Overview Of Aquarium Equipment List

Let’s go through a brief review of what essentials you need for your aquarium and its function. It will help you to see and understand why having a battery back-up is so important for your fish and their health.

Aquarium Filters

The basic function of your filter system is to keep the water clear and free of most debris; leftover food, fish waste, and other toxic components in the tank. They can be mechanical, chemical, biological, or all 3 in one filter. When choosing your filter, get the best that you can afford and the optimum one for the size of your tank.

I feel it is the top priority in a fish tank because if you don’t remove the waste then the water becomes polluted and your fish can get very sick. Your choice of substrate works along with the filtration system because it can grow the beneficial bacteria that help to remove the toxins from the tank.

Aquarium Heater

Your heater, of course, is going to keep your tank water at the prime temperature for your fish. If you are lucky enough to have fish that don’t need a heater then that will be one less thing to worry about if your power goes out.

If you keep the space where your tank is set up at a consistent temperature, then depending on the species of fish, you may not need a heater. Most fish need the water at 76-80 degrees. But there are some fish who love water that is a few degrees cooler. Your heater being out during a power outage could also be a huge concern.

Aquarium Lighting

The lighting is not near as important if the power goes out unless it is out for more than 3 days. Fish are used today and night when they are in the wild and that is what your lighting mimics in the tank.

If your power goes out at night, it will not affect the fish, because it will be just like you turning off the lights at bedtime. If the power goes out during the day, the house is light, mimicking daytime. If you need to, and the sun is not directly hitting the tank, you can open the curtain to give the fish more light. 

Your Aquarium And Power Loss

We will now begin to discuss all of the very important things you will need to do in case of a power outage, whether it be 3 hours or 2 weeks. Long-term power outages, of course, are going to be more crucial for your fish. As long as your tank is not overstocked with fish, you will be ok for about 24-36 hours with some slight interventions.

You spend a lot of time, money, and energy to set up your aquarium and to keep it maintained for the enjoyment of your family and visitors. Without some emergency precautions in place, all of that can be lost in just a matter of a few hours. 

Aquarium Temperature

Fish are like humans, we all have a certain temperature that we prefer to keep us warm and comfortable. If we are too hot we are miserable, if we are too cold we are miserable. There is a fine line for us and for fish where we are happy.

The only difference is, if we get cold we can put on extra clothes or jackets to warm back up. Our fish, unfortunately, do not have that option. So when the power goes out your glass aquarium is going to quickly adapt to the changing temperature in the room. 

If you have a spare blanket or two, preferably thermal, you will want to get your tank wrapped up as best as you can. Glass tanks are not very good insulators. Wrapping blankets around the tank will at least slow down the decrease in temperature.

You could also consider purchasing, or switching to an acrylic tank. These are great insulators and would stand up better if the power were to go out. Make sure that once the power is restored, you slowly adjust the temperature in the tank. If you adjust it too quickly or all at once it will shock and stress the fish, causing them harm. 

Aquarium Oxygen levels

Another huge factor when you have a power outage is the oxygen levels in the tank. Oxygen levels will decrease as the water temperature rises. This is where your filter comes in. Circulating the water and providing oxygen. Lower tank temperatures will actually hold more oxygen and it will also slow down the metabolism of the fish.

If you want to increase the oxygen during a power outage, extract some water out of the tank using a cup. Then slowly pour it back into the tank. You can do this once or twice an hour. This will keep circulation in the water, which the fish need. 

Aquarium Filtration

This is going to be the biggest, most important concern above all else if you have a power outage. If you have a battery back-up pump you need to get it hooked up as soon as possible. Your bio wheels can be submerged into the tank. You can also pour water over the filter media every hour to help with filtration. 

Closed and canister filters should be immediately disconnected. If you don’t, they can produce toxic substances, like ammonia, fairly quickly. Make sure that once the power comes back on, you clean your filter thoroughly before turning it back on in the aquarium. This will get rid of any of those toxins that built up while the power was out. 

Side Notes On Aquarium Power Out

Other things that you need to know when you have a power outage;

  • Do not feed your fish during a power outage. Fish can last up to 5 days without food. In the event that you do have to feed them, you are going to have to siphon the tank and do a 20% water change when the power comes back on, because of any food waste and fish feces. 
  • Watch out for disease. Power outages are stressful on your fish and therefore this is a perfect time for a parasite to attack a weaker fish.
  • Place Algone in your filter during and after the power outage. This controls the ammonia in the filter and helps keep the leakage into the tank minimal.
  • A power back-up system will provide energy to your filter. You can actually use a car or boat battery to make this happen. 

How Long Can Your Fish Survive Without Power

This is all going to depend on how your tank is stocked. If you have a fish tank that has just the right number of fish for the size and water capacity, then fish can last 24 to 36 hours. In the same tank, if you have it overstocked with fish, then you can expect to see your fish start dying in 3 to 9 hours.

You will have to perform a few interventions during a power outage to help your fish through this stressful time. You need to first insulate your tank with blankets, which we covered in the last section. You also need to keep the ammonia levels down, which was also mentioned above.

A lot of the preventative and emergency measures you take are going to depend on the length of the power outage and if you knew it was going to occur. Remember, your time is 24-36 hours if your tank is optimally stocked. Overstocked and you have considerably less time.

Aquarium Battery Back-Up

If you have the extra cash to spare, when you are purchasing all of the items for your aquarium, it is highly suggested that you go ahead and pick up a back-up battery pump.

They can run for several hours and normally require 2 D batteries. Battery back-ups are also very simple to use and can help save the life of your fish.

The air pump will cause some circulation in the aquarium and creates surface agitation which will help replace C02 with oxygen. As mentioned above, you can also use a boat or a car battery to power your tank pump during a power outage. 

There are a few different “formats” when your talking about battery back-up systems for your aquarium;

  1. Uninterrupted Power Supply (UPS)
  2. Aquarium Specific Battery Back-Ups
  3. Battery Powered Air-Pump
  4. DIY Battery Back-Up System

Any of these will work in slowing down the decrease of oxygen, water temperature changes, and rising ammonia levels when you have a power outage. 

There are many things you need to know when choosing your back-up system for your aquarium. Unfortunately, we do not have the convenience of delving into this at this point in time. So please, do a lot of research before purchasing the above back-up systems. We will discuss a few in detail, but there is a large variety of information that we are unable to cover today.

Emergency Power Supply for your Aquarium

This category and the back-up battery section go hand in hand because it is pretty much the same thing. The emergency power supply, in most cases, is going to be some form of a battery back-up.

If you are aware that a power outage will occur, it is so much easier to get your aquarium prepared. But if there is a storm, an accident that knocks out a power line, or some other incident then you will have an emergency on your hands when it comes to your tank.

With those types of situations, you have absolutely no idea how long the power may be out. Here are the items that you need to have and the action that has to be taken as soon as you can.

If you happen to live in an area with harsh storms or hurricanes, you have probably already purchased a generator or 2. In those types of situations, you could end up going without power for weeks or even months. With a generator, your fish will last a lot longer than the 24-36 hours. There is only so much intervention that you can do in that time frame to help your fish, without any kind of back-up.

In-depth, here are 5 things that you can choose from, to have on hand when you have an aquarium if the power goes out. Some are for short-term power outages and there are a couple that will work for long-term (over 3 days).

Battery Powered Air-Pump

We have talked about this option in a couple of other sections of this article, but briefly. Here, I will go into a little more depth and detail about this option.

The one thing that your tank (and fish) need is air. Proper air exchange equals good flow in the tank and agitation at the surface. When you have a power outage your gas exchange goes away too. The sooner you can get the water movement going again the better off your fish will be. Especially if you had no knowledge of the outage.

The battery-powered air-pumps are inexpensive and should be a must-have if you are going to have an aquarium in your home.

How Many Types Of Aquarium Battery Powered Air-Pumps

There are 2 types of battery-powered air-pumps, manual and automatic.
With the manual type, all you need to do is put the batteries in it, submerge the tubing down into your tank, and turn it on. This will create bubbles. As the bubbles rise it produces movement and agitation in the water, allowing for some exchange to take place.
The automatic air-pump runs on 2 size D batteries but also has a power cord. This will run off of your main power supply, but if there is an outage and you’re not home, this automatically switches to battery power if there is an outage. Saving you the stress and worry about your fish.

VorTech Battery Back-up

This type of back-up runs off of a DC current. In the event of a power failure, they will switch over to battery back-up mode. They also have the ability to switch to energy-saving mode, which will help the battery last longer.

The VorTech can run up to 2 pumps at once. A single battery back-up can run a VorTech pump for 72 hours. In most tanks a single battery back-up is sufficient, but you can hook up 2 to extend the run time.

If you purchase a VorTech pump and the VorTech battery back-up, then you can have your tank all ready to go, from day one, in case of a power outage. 

Tunze Battery Back-up

Just like the EcoTech VorTech, these also work on DC voltage. These work no matter what, but may be easier if you also have a Tunze controllable pump already hooked up to your tank. Just like the others, this runs off of your main power supply and will automatically switch to battery back-up in the event of a power outage.

Aquarium Power Inverters 

The above battery back-ups were the short term solutions I had mentioned at the beginning of the section. But what if your power goes out due to a storm and doesn’t come back on for weeks? You are going to need something more substantial and longer-lasting. Because not only do you need to worry about the oxygen in the tank, now you have to worry about the heat and the lighting. 

The power inverter is extremely handy for those cold winter months when your power goes out. If it happens during the warmer months you really do not need to fret over the water temperature aspect.

You can normally find a power inverter at an electronics or hardware store. Power inverters can be a good option if your power outages last more than 2 days, but less than 2 weeks.

Power inverters are rated by the amount of power they put out. So in order to run a heater, lights, and a pump you will need a sizable one. The downside to a power inverter; you are running all 3 elements in your tank, so the battery may not last long.

Generators For Aquarium Power Outage

Obviously, if you live in someplace that has severe storms and the potential for hurricanes, you probably already have 1 or 2 of these. With an aquarium, or not, you can not go weeks (or even months) at a time without power. The size of the generator, like the power inverter, is going to depend on how many things it has to keep running.

If you can afford it or need it, you can purchase generators that will back-up your whole house. These run off of natural gas and automatically switch on and power your entire house in the event of a power outage.

If you do not live in an area with severe storms and hurricanes, you can purchase a lot of smaller generators that can be used to power the 3 elements of your tank, in the event of an outage that will last a few days. 

The ultimate solution would be, if your wallet can handle it, of course, is to have a battery back-up on the aquarium that automatically comes on and a generator. This way, if you are unable to get home right away or in a reasonable amount of time, your battery back-up will keep the tank stable until you can get home and evaluate the situation. Then, if need be, you can power up your generator.


If you have an aquarium you NEED to have some sort of battery back-up or emergency plan in case of a power outage. In an optimal stocked fish tank, your fish can last 24-36 hours with a few small interventions. If your tank is overstocked then unfortunately you are going to begin losing fish in 3-9 hours. 

No matter the time frame, it is highly suggested, that you have some kind of battery back-up for your aquarium, to help protect your fish and the health of the tank. Whether it be a manual or automatic back-up or a generator, it can save you money in the long run by not having to replace your fish because they do not survive the power outage. 


I'm passionate about fish pets and love sharing everything I learn about them.

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