How Long Can A Reef Tank Go Without Power?

If you own a reef tank the words power outage is something that you never want to hear. 

A power outage can happen at any time and usually, it is unexpected. 

I know for me personally, the power tends to go out at the worst possible time. 

Worrying about how to keep your reef tank alive when the power goes out can be very stressful. 

It doesn’t take long for things to turn bad in a reef tank If you are not prepared for a power outage.

Fortunately, there are a variety of things you can do to ensure your reef tank stays healthy once the power goes out.

But in order to do that, you need to know how long a reef tank can go without power.

There is no exact amount of time a reef tank can go without power. There are too many variables. Every tank is different. But on average you can expect your fish to suffer from oxygen depletion in as little as 4 hours. If you have corals in the tank, they will start having health problems after 2 days without light.

These are approximate numbers and as mentioned, every tank is different. 

Power outage concerns

There are a few areas of concern if the power goes out. It’s important to know why the power went out in the first place.

The way you deal with it will be completely different depending on the length of time for the power to be out.

If the power will only be out for a short period of time due to a planned outage, you may not need to do anything.

If it will be out for a longer period, you may need to use a battery backup to keep things running.

If you know that a storm is on the way and the forecast is for a long term power outage, then you really need to prepare for backup power for a few days.

A generator would be required in this case. 

The problems that you will run into include:

  • Low oxygen levels for livestock
  • Increased levels of ammonia
  • Beneficial bacteria begin to die
  • Change in water temperature 

All of these items are cause for concern. 

Factors affecting the amount of time a reef tank can go without power

  • How much bioload – fish and corals
  • Tank size
  • Temperature
  • Last water change

The biggest factor in determining how long your tank can go without power is how much bioload your tank has.

If you have too many fish in the tank, your oxygen levels will deplete much sooner than a tank that is lightly stocked.

Reef Tank

Larger tank sizes with more water volume can normally last longer than smaller tanks. But this will depend on the stocking levels as well. 

Depending on where you live and the temperature of the room, can make a huge difference in how long you can leave the tank running without power.

If you live in a very warm part of the world where temperatures are hot, you probably are using a chiller to keep the water temperature within the normal range.

Without that, your water temperature will get too warm for the tank. Just the opposite happens in colder climates.

It doesn’t take long for your tank water to become cold when sitting in a cold room.

Also, consider when your last water change was completed. If you recently performed a water change just prior to the power outage, it’s more beneficial and the tank will be able to go longer compared to a tank that hasn’t had a water change in the last week or so. 

What to do in the event of a power outage?

Anyone who is planning to keep a reef tank should always be prepared for a power outage. Having the necessary equipment on hand can save you a huge headache and a lot of money. 

One of the most important items to have is a battery backup.

These are designed to allow specific equipment like wavemakers to keep running like normal if the power goes out. 

There are different types and brands of battery backups available. If you are using Ecotech equipment, I recommend you use the Ecotech Marine Vortech backup.

These are for use with all Ecotech pumps and can keep them running for up to 60 hours. 

Check them out at Marine Depot here.

Another great option is the IceCap battery backup. These will keep your pumps running for up to 17 hours. 

Water movement is the most critical factor to address if the power goes out. A battery backup is a convenient and affordable way to keep your water moving in the tank. 

Read more on battery backups here.

One thing you don’t want to do is feed your fish.

Most people overfeed their fish and overfeeding causes many problems with saltwater tanks.

Your fish can go a few days without food if needed.

Actually, they can go a lot longer than that. Most power outages are not any longer than a few days so don’t worry about feeding them if that’s the case.

Your water quality and oxygen levels will be depleted even more with unwanted food sitting in the tank. 

If water temperature is a concern, you have a couple of options. If the water is too warm and you need to cool it down, you can add ice packs into the tank or put ice into freezer bags and place them in the water. 

You can also make sure that your windows are open if there is a cooler breeze and close the blinds to prevent sunlight. 

If your water is too cold and you need to warm it up, you can plug your heater into the battery backup.

You can also wrap the aquarium in blankets and keep the lid closed on the tank as much as possible. 

Did you know? Quarantine tanks can be very simple to set up. Read more here.

If you have a stove or barbeque, you can make warm water and place it into bottles. Then set the bottles in the tank water to raise the temperature. 

If your tank is in a separate room, keep that room closed up and prevent cool air from getting in. 

Another piece of equipment that is very helpful is a battery-operated air pump with an air stone. This will provide water surface agitation and oxygen.

Keep extra batteries on hand as these air pumps can deplete them quickly.

You can actually buy an air pump that plugs into your wall and is designed to turn on automatically when the power goes out.

These are very effective in the event you are sleeping or away from the house when the power goes out.

They will turn on automatically and save your tank until you can address it. They are not meant as a long-term solution by they are a lifesaver that is very cheap to buy. 

Check out the Penn-Plax battery back up pump on Amazon. 

Water change

If the power goes out and you have the option to perform a water change, you should do it. Not only is this good for oxygen levels, but removing poor water and adding clean and new water is better for the fish and corals in the tank. 

Read: Can you have too much flow in a reef tank?

Move fish to another tank

If you happen to have a spare tank that you can use, consider splitting up the fish into different tanks. Lowering the bioload in the tank will be beneficial.

Just keep in mind that you will need to keep additional tanks running. 

Agitate water surface

This is a manual procedure where you will create water movement and surface agitation. Use a pitcher or container of some kind to scoop up water and dump it back into the tank.

The more often you can do this will be best. I have spent many long nights doing this when I wasn’t prepared for a power outage.

But you gotta do what you gotta do right?

Use your car for power

This is a great option if your vehicle has the ability to plug in a power cord. As long as the car is running you should be able to run a wavemaker and heater off of it.

You can also use an inverter attached to the car battery. Plug your equipment into the inverter to keep them running.

Here is an affordable inverter that works great on Amazon.

Remember to put gas in your car before the power outage!

Use a generator

The best thing you can do for your tank in the event of a power outage is to have a generator on hand.

This is the most convenient and stress-free way to handle it.

Many generators can run your whole house when the power goes out and this includes all your equipment for your reef tank.

A generator specifically to run your tank doesn’t need to be expensive or high end. It just needs to run your most important items for the length of time the power is out.

Just keep some extra gas on hand and you will be all set. 

Using a generator like Westinghouse is an affordable option that is available on Amazon. 


Losing power when you have a reef tank is no joke. It can cause serious problems to the livestock in your tank which is very expensive to lose. But as you can see there are many different things you can do in the event of a power outage to keep your tank alive.

The length of time that your tank can go without power will vary but anything more than a few hours will need to be addressed as livestock will begin to suffer and die.

Don’t be caught unprepared for the next power outage whether it is planned or unplanned.

Having the knowledge and equipment on hand will go a long way in saving your tank.