Is It Needed For A Fish Tank Filter To Be On All The Time?

The filter is a necessity in a fish tank. It runs for the most part every single minute of the day. It filters the water but it could be some noise coming from the filter. Is that filtration necessary to have on all the time?

Does a fish tank filter need to be on all the time? It’s recommended to keep the filter running at all times. Your fish will probably be fine, for it to be turned off a few hours. There is a risk of nitrate and ammonia spikes if off for too long.

In some circumstances, you just want to turn the pump to the filter off. There are even circumstances where the filter needs to be turned off. In this article, we will go through every single situation where you want or don’t want to turn the filter off.

How Is The Fish Tank Filter Working?

The filter is driven by the pump, pumping water from the fish tank, through the filter, and out through a nozzle. That’s how the most common type of filter is working.

The most common type of filter is a container inside (or hanging on the side of the fish tank) with the filter media inside.

The filter media could be of a lot of different types of material. One of the best types of filter media you could have is ceramic rings or balls. Other types are sponges which is the most common type of filtration.

The reason it’s recommended to have the ceramic rings or filter balls is that they have a lot of small holes for bacteria to live in while it’s easy enough for the water to go through the media without it being obstructed.

Sometimes the sponge filter could hinder the water flowing through making the pump work harder than needed.

The filter media has a lot of small holes where bacteria are living. It’s these bacteria that are doing the most important part of the filtration.

They are neutralizing the nitrate that’s building up inside the fish tank. It’s the nitrate that will kill the fish and are the main reason for the filter to be in the fish tank in the first place.

The filter media are also a physical barrier where dead leaves and other debris are collecting “cleaning” the tank.

These leaves and debris are important for you to remove while doing a water change. Otherwise, the debris will collect and during the breakdown of the debris, you could get an ammonia spike, killing all your fish.

To suck in the water through the filter the pump is having a propeller rotating, creating a suction sucking in the water through the filter and the pump.

To know that your filter is working, just look at the air pump nozzle if it spits out water. As long as the water comes out from the pump, that water has gone through your filter.

Also, take a look at your nitrite levels. If they increase, the filter is not working properly.

On my recommended tests page, I have some products I recommend for testing the water and specifically the nitrate test.

What Is The Fish Tank Filter For?

The fish tank filter is an important piece of equipment that you need in a fish tank. What it is used for is to filter out debris from the water. But maybe the most important role of the filter is to neutralize the nitrite that is building up due to the excrements from your fish.

The filter has one more important task. It’s to filter out any debris or material, preventing it from getting into the pump and destroying it.

The filter as a nitrate neutralizer

The most important task is to cycle the nutrients with the help of the bacteria living in the filter media. The bacteria are preventing ammonia and nitrate to accumulate.

Those are substances that, if they get too high, are life-threatening for the fish in your fish tank.

If you stop your pump, the water will not filtrate and the ammonia and nitrate are building up.

If you have a lot of fish, it will accumulate quicker than if you have a few fish. Therefore it will probably be fine to have the pump off for a few hours if you have a few fishes. If you have a lot of fish, the build-up could be so quick, it could cause a problem.

The nitrate and ammonia are building up from waste from the fish and also dead plants, and food that is not eaten.

If you feed your fish too much and turn the pump off, you will get a quicker accumulation of nitrate and ammonia.

The same goes if you to have a lot of plants.

The pump needs to be on mainly to let the bacteria living in the filter do their job of making ammonia and nitrate to be safe for the fish.

The filter to remove debris

The second task for the filter is to filter out any debris like dead leaves, uneaten food, and other organic material that will accumulate at the bottom of the fish tank.

The pump will suck the debris from the bottom through the filter where the debris gets stuck and start to be composted by the bacteria.

As you see the bacteria has a crucial role here too. Now it’s best to remove the leaves and debris while doing a water change. That’s because the breakdown of it by the bacteria could make the water parameters go bad.

If you didn’t have a filter between the pump and the water being sucked in, all the debris would get stuck in the pump and destroying it pretty quickly.

So you could say the filter is also a protection for the pump to get stuff stuck inside its propeller sucking up water.

Types Of Filters For A Fish Tank

There are some different types of filter you could have on your fish tank. The most common ones are:

  • Internal Filter
  • Hang On The Back Filter (HOB)
  • Canister Filter
  • Undergravel Filter

All these types of filters have their upsides and downsides. But they all do the same thing basically. They all are a house for bacteria to live and help with the water quality.

Internal filter

The internal filter is one of the most common types of filters. It’s those kinds of filters that have to be completely underwater to work.

They also use a pump to drag the water through the filter. The pump is pumping the water out through a nozzle making the water move and are helping with the oxygenation of the water.

The movement of the water caused by the pump is also moving the water towards the intake of the filter helping the water in the whole tank to get cycled through the filter.

The internal filter is cheap and you can put your fish tank against a wall. That means you could get a filter while on a budget and you are also able to put your fish tank in a corner of the room. This could make it easier to prevent the sun from shining on the tank.

I have an article on why you should prevent the sun from shining on your fish tank if you want to read why that’s a good thing.

The internal filter is also easy to maintain making it a good option for the beginner.

The downside of an internal filter is that it could destroy the look of your fish tank. It will be a big thing in the corner of your fish tank.

Be sure to put the filter somewhere where it will not obstruct the view of the fish tank. Some brands producing fish tanks are gluing their internal filter on, making it hard for you to remove.

This could cause some problems depending on where you want to put your fish tank in the room.

Hang on the back filter (HOB filter)

The HOB filter is very common too. It is commonly used by fish keepers keeping small fish tanks.

This type of filter is a canister containing the filter media that you put on the back of the fish tank. This makes it hard to put the fish tank against a wall. You need some space behind the fish tank to be able to fit the filter.

An upside with this type of filter is that, if finding a way to have the filter without it showing from the sides, it’s quite invisible while looking at the fish tank.

It’s not a lot of power with a HOB filter though. They are very low power and are suitable for the small fish tank or for someone on a budget since they are cheap.

The HOB filter is also a good type of filter for the beginner since it’s easy to maintain.

If going with a HOB filter, you get the necessity of filtering through the media inside the canister behind the fish tank but be sure the power of the filter is enough for the size of tank you keep.

I recommend a bigger size tank of at least 50 gallons (180 liters) since it’s easier to keep the water balance.

If you have this size fish tank, be sure the HOB is made for that size. The bigger you go, the harder it will be to find a HOB filter that is powerful enough.

Canister filter

The canister filter is more common with more experienced fish keepers.

That is because the canister filter has a lot of options to choose from with the filter media. There are a lot of different media to add to a canister filter.

It’s also because you will have good water flow with a canister filter. This is required for more advanced types of fish tanks such as fish tanks keeping African cichlids. The African cichlids need a high flow rate and then the canister filter is providing it with ease.

The canister filter is also a type of filter that will last you for a long time. That makes it a good investment since you don’t have to buy a new one because the pump is broken.

The canister filter could be quite expensive in the beginning though. If trying out the hobby of keeping fish, you should probably start with any other type of filter.

The canister filter will also take up a lot of space. You need additional space to put your filter except for the space your fish tank will take.

An upside though is that you will not have anything obstructing the vision inside of your fish tank.

The canister filter will also do the job of filtering the water and also add a hefty water flow, which some fish needs in a fish tank.

Undergravel filter

This is a type of filter that you put under your substrate. The water is pumped through the substrate into the pump and back out into the tank.

It’s not a very common type of filtration but it’s a very good type of filtration.

That’s because the filtration is caused by the substrate which is a very good filtrate media. Have you ever been to the mountain and you drink the purest, best-tasting water there is? That’s because of the filtration from the rocks in the mountain the water is flowing through.

That’s the same principle for the under gravel filter.

This makes the flow of water very slow which is good for fish that need less water flow in the fish tank.

The under gravel filter is also cheap to buy and are not obstructing the view of the fish tank.

The downside is that you have to put it in before you put anything else in the tank. You have to decide on the under gravel filtration before anything else.

You could also connect a canister that is outside the fish tank for additional filtration, taking up space in the room. So if you live small it could be a problem. Also, the media you put in the canister has to be changed quite often.

Another downside of the under gravel filtration is that solid particles will get dragged down, obstructing the flow making the under gravel filtration less effective.

No matter what type of filtration you choose, it will do its job of filtrate particles and be a house for the bacteria living inside the fish tank.

Just be aware of the downsides and try to prevent them the best you could in order to prevent any problems with the water.

What Happens If The Filter Is Turned Off?

If the filter is turned off the water will stop flow through it making the bacteria inside the filter almost useless.

The debris, leaves, and particles will collect at the bottom risking the water quality of your fish tank making it potentially deadly for your fish. This could wipe out your whole population of fish if you are unlucky.

The ammonia and nitrate will build up and get a problem for your fish. This is very dangerous for them too and if you get a spike of ammonia or nitrate, your fish will certainly die.

By keeping the filtration on at all times you will prevent these kinds of problems.

These problems will occur. How fast it will occur is depending on the amount of fish you have, how many plants you have, how much you feed your fish, and how your bacteria flora is inside the fish tank.

In What Situations Do You Have To Turn The Filter Off?

There is not a lot of situations where the filter should be turned off.

The only situation where the filter should be turned off (alongside the heater) is when you do a water change. That’s because if the water level gets too low, the pump inside the filter will get overheated and potentially gets damaged.

It is when it gets damaged you will have a problem so during the hour you do a water change, it better to turn the pump off.

During the water change, the ammonia and nitrate will not be able to build up. It’s during such a short time that you will be fine. Don’t forget to put it on after you are done!


The filter should be on at all times.

If turned off, you run the risk of getting ammonia or a nitrite spike, and potentially kill all your fish. The filters are not making a lot of noise so there is really no point in turning it off.

The only situation you should turn it off is when doing a water change. That’s because there’s a bigger risk of the pump breaking than it is getting a spike in nitrate or ammonia.

How fast the spike will occur while turning the filter off is depending on a lot of factors. Just be sure to feed your fish the right amount, don’t have too much fish, and monitor your water parameters.

Even if you do all this, you have to leave your filter on!


I have been a fish keeper a big part of my life. During the years I have gathered and searched a lot of information about fish keeping and here, on the website, is where I share that information to help you with your fish keeping. I want to provide the information that I didn't get when I had a question about my fish tank.

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