How Long Can You Leave A Fish Tank Filter Off? Full Guide

As an aquarium enthusiast, you've likely wondered how long you can leave your fish tank filter off without jeopardizing the health of your fish. It's a common concern among fishkeepers, and understandably so. Don't worry, though - in this post, I'll walk you through everything you need to know to keep your fish healthy and happy, even when your filter is switched off.
How Long Can You Leave A Fish Tank Filter Off

With ever-rising energy bills, some fish tank owners are looking to leave the filter off at night to save electricity, or you may live in an area prone to power cuts or need to switch your filter off while bug-bombing your home.

Others, like me, are noise sensitive and get driven nuts by the noise filters can make. If that’s you, I’ve done some great tips on reducing the filter noise further down.

Whatever the reason is for not having your filter running, I’ve gone over how you can keep your tank and fish healthy in this situation.

How Long Can You Leave A Fish Tank Filter Off?

There’s no set rule, it all comes down to the size of your tank, fish numbers, how many plants and decor items you have, etc.

TL;DR – I wouldn’t turn a filter off for more than a few hours, and it would only be on essential occasions.

Without a running filter, oxygen levels will quickly deplete, and the beneficial bacteria inside your filter won’t be able to remove toxins from the water, which will eventually screw up your tank’s nitrogen cycle.

Also, any fish waste and leftover food will be left to float around in the water rather than being trapped in the filter, so you’ll end up with a dirty-looking tank and an ammonia spike in no time.

The Importance Of A Fish Tank Filter

A fish tank filter is a vital part of your aquarium setup and is one of the major factors in maintaining a healthy tank environment.


Fish and beneficial bacteria, just like us, require oxygen.

The filter’s outlet creates surface agitation which allows carbon dioxide to leave the water, and fresh oxygen to enter. This process is called gas exchange and is very important to keep the aquarium healthy.

Fish laying at the bottom of the tank or gasping at the surface could be a sign that there is a lack of oxygen in your water.

Water Quality

A fish tank filter uses three types of filtration: mechanical, biological, and chemical.

Fluval Filter Media

Mechanical Filtration 

Physically traps and removes solid particles such as uneaten food, fish poop, and other debris from the water.

Biological Filtration 

The process where beneficial bacteria break down harmful ammonia and nitrite, which are byproducts of fish waste and decaying organic matter. 

These bacteria live on media inside your filter (and other surfaces in your tank), not in the water as many people believe, and rely on a continuous flow of nutrient-rich water to efficiently do their job and thrive.

Chemical Filtration (Optional) 

Zeolite and activated carbon help to remove chemical impurities, odors, and discoloration from the water, keeping it crystal clear and odor free, no one wants a stinky tank!

A couple of things to be aware of when using chemical filtration is that you need to change it after around one month as it can’t be cleaned like mechanical filtration. 

If you are treating your tank with medication, remove the chemical filtration first as it will absorb the medication.

Mechanical Removes debris and particulates Foam, sponges, floss
Biological Supports beneficial bacteria Ceramic rings, bio balls, lava rock
Chemical Removes contaminants Activated carbon, zeolite

Fish Tank Filter Sizes

A general rule of thumb is that you want the pump output (gallons per hour) to be 5 times the size of your tank, so multiply the size of your tank by 5 to find out the g/ph that is ideal.

I’ve found that following this simple calculation stops you from buying a filter that is too small or too large (and wasting money) for your aquarium.

If you have an overstocked stocked tank that has a large bioload, it’s recommended that you multiply your tank size in gallons by 10, to find a suitable turnover rate for your tank.

20 100 g/ph 200 g/ph
29 145 g/ph 290 g/ph
40 200 g/ph 400 g/ph
55 275 g/ph 550 g/ph
75 375 g/ph 750 g/ph
90 450 g/ph 900 g/ph
100 500 g/ph 1000 g/ph

Most manufacturers state the g/ph when the filter is empty with no media in place. 

Once the media is in place (and it’s got gunked up after a while!), these g/ph figures reduce drastically and the real-world turnover rate will probably be around 50% less. 

Nonetheless, I’ve found on the whole that the filtration based on this calculation is more than adequate.

Factors Affecting Fish Survival Without A Filter

There are a few other things that will determine how long a fish can live without a filter.

Live Plants

Planted Aquarium

Having live plants in your aquarium can make quite a difference in your fish’s ability to survive without a filter.

Plants provide natural filtration by absorbing ammonia, nitrites, and nitrates, making the water safer for fish. They also release oxygen, helping to maintain adequate levels for your fish to breathe.

One of my favorites is the pothos plant, as it does a great job of absorbing toxins.

Duckweed also does a great job, but it takes a lot of maintenance to keep it under control.

Water Temperature

The temperature of the water in your tank can have a significant impact on how long your fish survive without a filter.

Warmer water holds less dissolved oxygen, making it more challenging for your fish to breathe.

If the water becomes too warm without proper aeration, it may reduce the amount of time your fish can survive without a filter running.

When it comes to maintaining a steady temperature, I swear by the Fluval E series heaters. I’ve used them for years as they are reliable and well-built.

Fluval E100

Tank Size And Stocking Level

The size of your fish tank and the number of fish you have in it will influence how long your fish can survive without a filter.

Larger tanks typically offer more stable water conditions, allowing your fish to tolerate the absence of a filter for a longer time.

Lower fish stocking levels reduce the waste produced and the demand for oxygen, providing more time for your fish to adapt to a non-functioning filter.

If you have overstocked your tank, I advise that you keep your filter on all the time and change the water as often as required, even if it means doing a small water change every day.

Water Movement and Flow

Even without a filter, some water movement is necessary to agitate the surface and promote oxygen exchange.

You can create water agitation by using air stones, bubblers, or circulation pumps, which help oxygenate the water and prevent the buildup of harmful chemicals.

If you don’t have an airstone etc, it’s crucial you keep agitating the surface of the water during a power outage. Get a cup or jug and fill it from your tank and pour it back in, do this every 20-30 minutes.

Keep in mind the water flow requirements of your specific fish.

Strong water currents can stress slower-swimming fish, such as betta’s, and decrease their chances of survival without a filter.

Managing A Filter Shutdown

When it comes to managing a fish tank filter shutdown, there are a few considerations to ensure the health of your fish and the tank ecosystem.

Cleaning And Maintenance

You should clean and maintain your fish tank filter regularly to ensure proper operation.

While doing so, you’ll obviously need to turn off the filter temporarily. Don’t worry, this won’t harm your fish as it will only be for a short period of time.

When cleaning the filter media, use water from your tank (or use what’s inside your canister filter if you have one) as this helps preserve the beneficial bacteria while cleaning away debris.

TOP TIP: Don’t throw that water away when you’ve finished cleaning your filter and media. Use it to water your house or garden plants, they’ll love it!!

Power Outage Emergency

Power Cut

During a power cut, your fish tank filter will be off, it could be for 5 minutes to several days if you live in an area prone to storms.

This can be very concerning, as turning off the filter for more than a few hours may have detrimental effects on your fish and the tank’s ecosystem. No one wants to see their fish slowly suffocating. 

There are a few things you can do in this situation:

  • Monitor the power companies website or app for up-to-date information on how long the power will be off
  • Monitor your fish for signs of stress or adverse reactions
  • Regularly test your water for ammonia spikes
  • Reduce feeding your fish to reduce waste production
  • Increase oxygen flow by filling a cup or jug with tank water and pouring it back into the tank on a regular basis (every 20-30 mins) or use battery-powered air pumps
  • Check the water temperature, especially in winter. Wrap blankets or bubble wrap around the tank sides if temps drop too low. Do not fully encase the tank and cut off oxygen!

If the power cut is going to be a lengthy one and you’re facing the possibility of going days without a filter, change around 20% of the water in the aquarium every day.

Home Generator

This is one of those products that you put off buying because of the expense, but then instantly regret it as soon as you are in an emergency situation!

If you have a few aquariums or keep expensive fish and live in an area prone to power cuts, I highly recommend investing in a generator for emergency situations, it’s worth it to ease the stress and worry of power outages in general.

WEN 6000-Watt 120V/240V Generator

Battery-Powered Air Pumps

In the case of shorter filter shutdowns or power cuts, you could consider buying a battery-powered air pump.

These devices are cheap and a great item to have in stock to help maintain oxygen levels in your aquarium during emergencies.

The AquaMiracle lithium battery powered aquarium air pump runs on your mains power and features a built-in power-outage detector that will keep the pump running automatically when power is lost.

You could hook this up to a sponge filter to help keep the water clean and filtered, in longer power cuts.

AquaMiracle lithium battery powered aquarium air pump
AQUANEAT Aquarium Bio Sponge Filter

The lithium battery will last for 20-40 hours depending on the setting you choose.

It comes in 2 different sizes for aquariums of up to 60 gallons, and for up to 120 gallons.

When using a battery-powered air pump, make sure to check and replace the batteries regularly to ensure proper function

Can I Turn The Fish Tank Filter Off At Night?

It’s not a good idea to turn off a fish tank filter at night.

With no filter running, ammonia and other toxins will build up and could cause serious health issues for your fish.

Filter Noise: How To Make A Fish Tank Filter Quieter

If the noise from your filter is keeping you awake, or just annoying you in general, there are steps you can take to reduce the noise.

HOB Filter: How To Reduce The Waterfall Noise In Fish Tank

AquaClear HoB Filter

Ah, the HOB filter. I hate that waterfall noise they make, always makes me need to pee, or maybe that’s just my age!? Some people love the sound and find it relaxing.

To reduce the waterfall noise raise the water level so the water doesn’t have as far to fall back into the tank.

I tend not to use HOB filters because of this noise (I prefer canister or sponge filters), and if you’ve got a labyrinth fish like a betta, filling the tank water right to the top isn’t going to be practical as they need to breathe at the water’s surface from time to time.

If you’re looking to upgrade to a canister filter, the Fluval 07 series are my top recommendation as they’re almost silent when running and a breeze to maintain.

I’ve left links to posts about the Fluval 07 filters a bit further down, so you can pick the best one for your tank setup.

How To Make A Canister Filter Quieter

Fluval 407

Maybe you’ve already got a canister filter and want to make it quieter.

The vibrations from these things can drive someone insane!!!

Believe me, I’ve torn my hair out trying to figure out what was causing them, and over the years I’ve employed the following 5-step care and maintenance plan with great success – ah the sound of silence!

1. Clean And Lubricate The Impeller

Every time you clean your filter, take the impeller apart and make sure it’s clean and free of any debris or gunk.

Coat the impeller shaft and bushing very lightly with petroleum jelly.

Amazon Basics Petrolium Jelly

Make sure you apply only a very light coating. If you put too much on you could end up with an oily film in your tank water.

When you reassemble the impeller and housing, make sure it’s seated correctly and the impeller cover is fitted securely.

2. Don’t Overfill Your Media Baskets

While it’s tempting to cram as much filter media into your baskets, if you put too much media in, the basket that sits on top of it may not sit flush and can rattle around.

3. Add Some Padding

Take an old towel, fold it in half a couple of times, and stand your canister filter on top of it.

The padding from the towel will cut down big time on that awful humming vibration noise some canister filters make when they’re stood on a hard surface.

4. Make Sure The Filter Is Level

If you have something (the power chord for example) lifting one corner up, even very slightly, that’s going to cause a vibration.

5. Keep Away From The Edges

Keep the canister and hoses away from the edges of your aquarium cabinet. Those things can cause an awful vibration sound.

If that’s not cutting it and you’re looking at upgrading your canister filter, I highly recommend a Fluval 07 to you.

Fluval 07 Series Filters

Depending on what tank size you have, check out my Fluval 107 vs 207, and Fluval 307 vs 407 comparison posts.

Not only are they practically silent (48 dB for the 407 right next to it – yes I’m a geek and measured it!), but they’re also economical to run.

Approximate annual running costs for 07 series based on a cost of $0.20 per kilo watts per hour is:

  • 107: $17.52 per year
  • 207: $17.52 per year
  • 307: $28.03 per year
  • 407: $40.29 per year

Closing Thoughts On How Long Can You Leave A Fish Tank Filter Off?

Although some fish species can tolerate a filter being off for a limited time, it is generally not advised to leave your aquarium filter off unnecessarily.

Extended periods without a running filter can lead to a buildup of harmful substances and oxygen depletion, which can significantly impact fish health.

Prioritize your finned friends’ needs and keep the fish tank filter running 24/7 to promote a healthy environment for them to flourish.

Check out the aquarium health section for guides and tips to keep your aquarium in tip-top shape.

Picture of Paul


Hey, fellow fish enthusiast 👋! I'm Paul and I've been an aquarium addict since I won my first goldfish at the fair many years ago. Let me share with you the knowledge that I've gained along the way (and avoid the mistakes I've made!), so you too can create an underwater paradise for your aquatic friends.