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Should Aquarium Filter Always Be On?

This is a great question! You can look at this one from the perspective of does the aquarium filter need to be on for the fish’s sake and should a piece of equipment such as a filter be left running 24/7? Not surprisingly, this question comes up a lot online. I can help answer both sides of this question.

An aquarium filter should be left on 24 hours a day 7 days a week. Aquarium filters are manufactured to run continuously for years on end. A filter should be left on to provide movement in the water causing surface agitation for gas exchange. A filter draws organic materials such as waste and excess fish food out of the tank. And lastly, a filter provides beneficial bacteria a place to grow and thrive helping to keep your tank water healthy.  

That’s the main gist of the answer when it comes to leaving your tanks filter on or not. I know there are reasons you might want to turn it off occasionally and sometimes its just okay to turn it off for a bit. In this article, I will expand on why you should leave the filter on and why it’s okay to turn it off every once in awhile. I will also touch on other related questions you might have as I think of them. Let’s get started!

Why an Aquarium Filter Should Be Kept on Always (24/7)

Okay, here it is. There are a few reasons why you should keep your filter running constantly. Aquarium filters are not just for keeping the water looking sparkly clean or drawing in excess fish food or poop. There are other important reasons to use a filter all day/every day which we will go over now.


  • Water movement. Well, it is true filters do siphon out some of the floating debris and organic materials from the water. Things like excess food and fish poop are common. This means then that these organic materials would have to be cleaned out of the filter because even though it is technically in the tank, its still in the same water and this water flows from tank to filter and repeat.
  • Surface agitation is an important process in a healthy tank. When the water is moved, it can agitate the surface of the water. When this happens, it helps gas exchange. Carbon dioxide from the water is released from the water and when this happens, oxygen enters the water. This helps to promote a healthy tank. Live plants and the fish all require oxygen even though they live under water.
  • Home for beneficial bacteria. It’s well known that aquarium filters are where you can find living beneficial bacteria in your tank. It’s the beneficial bacteria that helps keep the water parameters in check, which in turn, keeps all inhabitants happy and healthy. It is important to know how to clean an aquarium filter properly or you will kill off the beneficial bacteria, possibly throwing the water parameters out of whack and putting your fish’s lives in danger! I have an excellent article on the topic. You can find a link to it at the bottom of this page.
  • Having your filter on all the time helps the water heater more easily regulate the temperature of the water. Some fish are hardier than others and can handle swings in temps just fine. Some fish cannot and they will get stressed and eventually die if the temperature swings are too great and too often.

There are some filters you can hook air tubes up to that draw air in and force it into the water. This helps with the water movement and surface agitation. It helps a little bit with adding oxygen to the water but not as much as surface agitation does.

There are other questions regarding having a filter on or off and I hope to have captured most of them to help you out. 

Can I Turn My Fish Tank Filter Off at Night?

If at night means 8 to 10 hours, then no, I would not recommend it. When the filter is off that long, if there is no powerhead running, then there is no surface agitation happening. The bacteria in the tank filter (if it’s a hang on back or cannister style) is getting colder because of no circulation and will start to die off. It’s just too long to risk something happening.

Now, chances are for one night, everything would be fine, I just wouldn’t get into the habit of doing this.

How Long Can You Leave a Fish Tank Filter Off?

Aside from a power outage at your home, I wouldn’t turn the filter off for any longer than an hour or two. It’s just my preference. If you need to turn it off to clean the filter or tank, that’s perfectly fine and unavoidable.

The only other reason I can think of that someone might want to turn the filter off is because of the noise and they can’t sleep. If that’s the case, then I suggest you move the tank somewhere else.

Will My Fish be Okay Without a Filter for a Day?

Yes, your fish will be alright with no filter running for one day.

If possible, have an air stone running to promote surface agitation and if you have a powerhead, let that run as well. Just having some movement in the water makes all the difference.

Be aware that wherever your heater is situated will be quite a bit warmer than the rest of the tank, if you have nothing moving the water around.

Is it Bad to Have Two Filters in a Fish Tank?

Not at all. Having two filters is an excellent way of making sure there is a lot of water movement.

Having that extra mechanical filtration will help suck up any organic compounds floating around.

Do I Need a Filter if I Have an Air Pump Running?

If you have an air pump just pumping air into the water, it might not be enough movement.

Unless you are running a corner filter off an air tube, then you are good to go.

If you can add in a power head for water movement, it would be beneficial to the health of the tank.

Can You Over Filter a Fish Tank?

I don’t think you can “over filter” a fish tank. I think you can have too much water movement, which some types of fish might not do well with. Betta’s, for example, do much better in calmer waters. If you have a Betta and it’s having a hard time maneuvering, check out the article link at the bottom of this page relating to this.

If anything, you can “under filter” a tank but over filtering, I don’t believe that’s a concern.

How High Should the Filter be in a Fish Tank?

Feel free to crank your filter up to run at its maximum potential. The more the water gets circulated the better. Most fish will enjoy the movement. Again, if you have fish like a Betta that don’t enjoy that, then check out my article listed below for a simple solution.

I hope you found this article helpful. Please check out the articles I have listed below or feel free to browse around the site for other interesting topics. Good luck!

Recommended Aquariums-at-Home Articles

How Often Should You Clean Your Aquarium Filter?

How to help if water current is too strong for your Betta.

Aquarium Set Up for Beginners.

Are Saltwater and Freshwater Filters the Same?

Why Do Fish Die After Cleaning the Tank?

Are Fish Tank Filters Noisy? (How to Fix)

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