How Does A Canister Filter Work & Why Should You Use it? Protection Status

Canister filters function by employing various filtering media to remove contaminants from the water of the tank. The water in the tank flows back and forth back to the aquarium through the outlet and inlet tubes at a steady flow rate.

If you are an aquarist and just learning about the maintenance system of your fish tank or turtle tank, you would know the importance of keeping your aquarium water clean. Out of many aquarium filtration types, one of the most popular ones is the canister filter. But how does a canister filter work? Well, we are about to find out more!

As we have already mentioned, several types of aquarium filters are available depending on your tank water. You can have a saltwater aquarium or a freshwater aquarium, while the common thing between these two is the appliance of the proper filtering system. But the question is, how to choose the right one? 

You can decide on your own If you know how these varieties have their own benefits. These might look complicated to you at first glance, but it would be much easier once you understand the basics.

Before we dive into how does a canister filter works, let’s clarify our concept of the types of filtration methods.

Filtration Methods:

How does a canister filter work and Canister filter filtration process

You can clean your aquarium water using one of three ways, biological, chemical, or mechanical. Each of these systems has different functionality and should be applied accordingly. The biological filtration process is necessary if you want to reduce maintenance time. 

Mechanical filtration maintains the clarity of the water, whereas chemical filtration removes toxic substances present in the system. There is also a chance of crystal-clear water being harmful to the fish or the dirty-looking water being safe!

Biological Filtration:

In this method, the beneficial bacteria and some other microorganisms convert the tank water’s waste products into less toxic substances. Fish living in the aquarium are bound to leave waste materials as they digest their feed. If the discharge does not get removed within a certain period, the water will become toxic, which is very harmful to aquatic lives. 

A biological filter turns the toxic ammonia into nitrite and then into nitrate. Too much nitrate in the tank water can cause problems with fish health. They are also responsible for algae growth. While nitrate is not deadly, you have to remove it from the water via frequent water changes. The process that helps to establish the biological filtration process is known as cycling.

Mechanical Filtration:

In this system, a specific type of mechanical filter is used as a mesh to clean the water by pushing it through. The mesh catches the floating particles that are unable to cross the openings. These filter materials can be a sponge, filter pads, filter floss, aquarium gravel, etc. Regardless of the material, the performance of mechanical filtration depends on several factors [know more]. 

Chemical Filtration:

In this one, special resins or activated carbon are used to remove tannins, medications, and impurities from the aquarium. If the chemical filter media becomes clogged with impure substances, they won’t be able to draw pollutants from the tank water anymore. 

When water passes through the resin or chemical media, the toxic chemicals are left behind. While this filtration method is a common one preferred by many, new products are developed using this method that can remove specific substances or extra nutrients from the water. 

What Is a Canister Filter?

The main purpose of aquarium filters is to remove chemicals, debris, and toxic substances from the water, preparing the bed for biological filtration. While several types of filters are available with distinct features, a canister filter is not the lesser-known one. As a matter of fact, this specific power filter system is quite popular.  

A canister filter is basically an external chamber that contains different filter media to sieve the water. The filter media uses the combination of a rotor and gravity to push the water through. The water gets inside the external canister filter via an intake hose. After getting filtered in the media, the water returns to the tank via a spray bar or spillway.

A motor, cartridge, and tubing are the three major elements of a canister filter. The main part looks like a cylindrical tool that has a pump and a filtration medium. This external filter stays outside the water tank and has two hoses attached to it. The intake and outlet hose go into the aquarium. The pump forces the water through the filter medium with efficiency. 

Generally, the chamber size depends on the tank size it is operating on. You have to place it pretty close to the water tank. Extended versions of this filtration method were once pretty famous for filtering drinking water for people. 

The key benefit of a canister filter is that the tubes connect the filter with the water source. Thus, it doesn’t touch the tank water throughout the filtering method.

How Does a Canister Filter Work?

How does a canister filter work? Thanks go to @TIAGO DOWNUNDER for this informative video

The mechanism of a canister filter is a pretty straight-up process. It uses a lift tube to draw up the water from the aquarium and pushes it into the filter chamber. There, the water passes through a series of filtration media to become pure. The path of the flow can be different for specific models and brands of the filter. 


Generally, you have to fix the external filter underneath a rack outside the aquarium. The basic construction usually consists of

  1. Inlet fitting
  2. Outlet fittings
  3. Filter media
  4. Vinyl tubes

The inlet and outlet tubes are adjustable, and you can spray bar, lily pipe, etc. to pump back the water. The in-tank pump or internal motor will power the filter that pushes water inside the canister. Once the filter is fully water-filled, the pump will force out water from the filter to go back into the filter outlet.

Internal Motor or In-tank Pump

Canister filter's Internal Motor
Internal Motor

An internal motor means no pump inside the fish tank, saving a lot of aquarium space. They are easy to clean while servicing, and you don’t have to go into the tank to clean a dirty pump. An in-tank pump will allow you to adjust the flow due to the smooth pump switching facility. With an internal pump, you have to operate at a specific flow rate.

Water Flow

The water flow through the filtration media is not absolute. Some units screen from top-to-bottom, while others do the opposite.

  • The water comes into the canister from the pump suction and passes down a cylinder, minimizing murky water gradually till it reaches the tank floor.
  • Next, the water leaves the cylinder and crosses different media trays.
  • While gradually getting filtered, the water comes out of the return tube to go back into the tank. Some brands may have chambers instead of media trays, but the end result remains the same.

Flow Rate:

Most of the time, people check the flow rate before purchasing filters. The capacity of the canister filter is crucial as you get an idea of the required turnover rate for effective cleaning. Measuring the peak height of the tank can give you an idea of how quickly the filter can flow at that height. Just think about your garden hose with no nozzle. 

If you point the hose upwards, the water will only go up some distance and fall back. For a higher stream, you have to increase the pump power or the water velocity. This same theory is applicable to canister filters. The more the water has to go, the more it will take time. In fact, the pump may not win against gravity if the traveling route is notably high! 

Siphoning Water:

This external filter can provide biological, mechanical, and chemical filtration based on the filter media you use. The basic principle of a canister filter is siphoning the water. The system is like how you clean the in-ground and above-ground pool using a water pump and a hose tube. It can be top-to-bottom, bottom-to-top, center-out, back-to-front, etc.

This method uses gravity to move a massive quantity of water from the aquarium to the canister. You have to put the garden hose to connect both in a U shape, through this water will pass from one another. The water entering the main chamber will be pressured by a pump, to cross the filer media and go to the other side. 

Multiple Filtration:

The filtration process of a canister filter is the unique trait that makes it different from other filters, and in a good way. While most regular filters have a single filtration process, a canister filter can have three filtration processes working together. Biological, mechanical, and chemical filtration ensures no waste, toxic substances, or debris remains in the tank water. 

They Are~
  • The technique is to pull the water from the tank and then expel it into the aquarium. First, the aquarium water is drawn in by the inlet tube towards the external chamber. The water starts going through a set of screening processes once it approaches the main compartment. The way of water flows will depend on the specific brand or model of the canister filter you are using.
  • Regardless of the direction, the mechanical filter inside the chamber starts removing organisms like bacteria, algae, wastage, debris, etc. The thickness of the media plays a vital role. The finer the mechanical filter media is, the smaller particles it would catch. But keep in mind, finer media can get clogged rapidly over time. Hence, you have to replace or rinse it to keep working.
  • Coarser media may not catch all the tiny particles, but they will take more time to clog. The biological filter media acts as a breeding surface for beneficial bacteria that consume toxic substances like ammonia and nitrite. This step will make sure the water remains healthy for the pet fish
  • The chemical filter media will absorb the harsh chemicals from the water. Once the water has passed through all the canisters’ filter media, it will be pumped back to the aquarium via the outlet hose. While having a water pump is a must for the sealed canister filters. Some of them may be built-in, whereas some are attached separately. They can improve water quality and reduce maintenance efforts at the same time. However, you have to check the water chemistry and change the water if necessary.


If you want your canister filter to work efficiently, maintaining the device is something you have to do frequently. The preservation of a canister filter usually depends on several factors the model and brand, type of media, etc. In most cases, you can use different types of filter media in a canister filter. 

Most of them have cartridges, media bags, baskets, or distinct chambers to keep in your preferred media to get the proper filtration for the fish tank. While some media needs to be cleaned out frequently, other media have to be replaced instead.

To get a better understanding of how to maintain the filter media, make sure to check the manufacturer’s instructions for that specific filter model. You have to regularly clean the pumps and the tubes of the canister filter as well.

Benefits of A Canister Filter

Canister filters are the most common and versatile water filter tool preferred by many aquarists. There are various types of advantages you can get while using this one. 

  • Versatility is one of the most lucrative features of a canister filter. Regardless of whether you have a saltwater or a freshwater tank, this filter works pretty well in both. 
  • If you are a turtle lover, you will probably know how turtles can make the tank dirtier and messier than fish. But due to its efficiency in keeping the water clean, you can use a canister filter in your turtle tank as well!
  • This filter is one of the most effective water filtering processes available in the market. Some premium quality filters can sieve out wastes from gallons of tank water per hour. Hence, you can use it for the biggest aquatic tanks without any issues.
  • With most canister filters, you can combine the biological, chemical, and mechanical filtering systems to get the best result possible. All these three mechanisms act together to execute the best purification for providing a healthy water environment. This is an exclusive feature of this filter. 
  • Another terrific benefit of this filter is the correct flow direction of the water at the proper spot. The media basket is responsible for this specific process. It also makes sure every water drop passes over the screening, giving you complete filtration. 
  • The mechanical filtration of this filter easily washes out all the polluted elements from the water.
  • The chemical and biological screening makes sure no traces of ammonia buildup and chlorine pollutants remain. And this is where the activated carbon does the magic!
  • Lastly, setting up a canister filter is a fairly easy process to follow and maintain. 

How to Clean a Canister Filter?

The proper ways to Clean Canister Filters

Cleaning a canister filter properly is vital to maintaining its quality. You can do the steps yourself if you know the whole process.

  • First, plan the cleaning time with the regular water changing schedule of the fish tank. To clean the filter, you can use the aquarium water at that time. 
  • Disconnect the water tank from the filter. Make sure all the connections of the filter are closed.
  • Have it in a place where you can easily wash it. Keep in mind that murky water will be spilled everywhere around the cleaning spot. Hence, choose a proper location to clean it. Now, open the connections to let the water flow
  • You have to detach the filter lid from the main body. Check for the screws that fix them together. If you don’t find the screws, check the instructions on the body. Once you find them, start opening the screws one by one.
  • After opening the screws, carefully take out the lid. You will see media baskets on the outside zone of the filter. You have to be very discreet while removing the filter lid.
  • If you rush too much, the media may fall from the basket during the opening stage. It means you will have to do extra cleaning along with the filter washing.
  • Now, separate the median and the basket from the canister. You will see multiple baskets attached collectively with rods. You have to open the rods and sever every basket. 
  • The canister is clear once all the baskets are taken out. You may see some ruins inside the canister. Clean it with aquarium water or a showerhead. Rinse it thoroughly so that all particles get washed out from the canister.
  • Empty the canister by removing the baskets. There should be some debris left inside the filter. A showerhead or aquarium water should be enough to clean this debris.
  • If you see any foam or pad remaining inside the cylinder, take them out and put them on the basin. Also, put the empty baskets in the sink.
  • Clean the foams and the basket and make sure both objects are completely clean. While rinsing them with water, you can see the ambiguity is going away. Continue the cleaning process until all the dark spots are faded.
  • After the cleaning is complete, place the foams back inside the filter. Put the baskets with the rods as it was before you detached them. Make sure it is rebuilt just as it was before you opened up the filter. 
  • Next, screw back the cover of the canister to its usual place and fill it with water. Now, again attach the filter to the aquarium water. Make sure the connections are locked until you have joined both objects correctly.
  • Now, unlock the valves and check the aquarium. If you see bubbles coming out from the inlet and outlet pipe, wait for it to finish. Once there are no bubbles in the filter, you may turn on the filter.
  • Wait for a bit to see any water coming out from the outlet hose. You have to make sure the filter is correctly attached like before. If you know this step is going on perfectly, it indicates that now your filter is clean. 
  • While you are cleaning the filter, remember that the pump and the tubes of the filter need cleaning as well. But it doesn’t have to be as frequent as the filter or aquarium cleaning. You can fix a time in a few months to cleanse all the parts. 

If you like to know more details about cleaning canister filters, you can read our other article How To Clean Canister Filter? [Simple But Important!]. Hope our experience will help.

Why Should You Use a Canister Filter?

Canister filters are very effective if applied and maintained proper way. A good quality filter provides you the chance to choose the filtration type suitable for your fish tank. You can customize the filtration media rather than using pre-made cartridges. Not to mention, these filters require lower maintenance than a similar type of power filter.

Besides, most canister filters pump back the water to the aquarium using a spray bar, thus reducing the current and evaporation. Keep in mind to change the activated carbon once it is immersed with particles. While the cost of a canister filter is slightly higher than the other filters, the features and benefits you get in return are unbeatable. 

You can use it for medium and large tanks as they can effectively purify a generous volume of water. However, make sure to remove the carbon if you are medicating the fish. Because an active carbon will negate the medicinal effect, thus preventing your fish from getting the proper treatment.

Although water leakage is a rare case, you should still make sure the valves are sealed to prevent such an event. There could be severe noise during the initial priming when the pump and the main chamber start siphoning water. It will be better if you relocate the fish once the first run is complete.

How to Choose A Canister Filter?

After discussing all the benefits of having a canister filter for your aquarium, you might be thinking about buying one immediately. This may look tough to you at first. But based on some simple criteria, you can easily select one from the available ones in the market!

1. Tank Size:

Before you pick the filter for your fish tank, you need to understand how much water you want to filter. It can be determined by the tank size and the water-containing capacity of the aquarium. Once you learn the exact quantity of water to pass through the filtering system each hour, check the filtering device’s labels.

Most people prefer a filter that can handle 6X more water than the tank size. However, if many fish types are present in the tank, you should opt out for the one that can range between 6-10 times. 

2. Water Pump:

The water pump is the key element of a canister filter. This pump continuously works on the clock unless you switch off the machine for maintenance purposes. And therefore, you should get a powerful motor with a standard impeller. Canister filters can operate using two types of engines, epoxy-sealed, and magnetic motors.  

The epoxy-sealed on is kept upside down and runs with electricity. The positioning of the motor makes it easier to remove the particles and debris with ease. The magnetic engine uses a magnetic coil as well, but there is also an auto-priming function included. This feature helps the water to flow consistently as well as keeping the aquarium free from pollutants.

3. Water Sealing:

A damaged valve can hinder the filtering process and cause more problems for you. You wouldn’t want any water leakage issues in the canister filter of your aquarium. The intactness of the valves is essential as the pump circulates a large volume of water every hour. Hence, you must check all the valve connections to ensure they are sealed properly.

4. Sound:

Aquatic animals like fish, shrimp, and turtles are very sensitive to loud sounds. It means the smallest increase in loudness in the water tank can cause unfavorable effects on their energy. It can affect their feeding cycle and the reproduction system as well. 

Hence, get a filter that has lower noise production. Fortunately, several premium-quality filters maintain a pretty quiet environment.

5. Brand:

While you can find hundreds of brands out there, a canister filter from a quality brand will always be more beneficial to your aquarium. The Fluval Fx6 and Marineland Magniflow are some of the best canister filters right now. Both brands come in various sizes and have great durability. 

6. Good Flow Rate:

To understand the efficiency of a water filter, you have to know the device’s flow rate first. An excellent flow rate will mean the filter is of good quality. Here, the flow rate means the number of water-cleaning cycles a filter can complete. A standard filter shall finish four periods per hour, but the filter size and pump performance also matter.

Types of Aquarium Filters [Additional Block]:

How to Choose The Right Filter For Your Aquarium!

Like canister filters, aquarium filters are available in many more forms. While some are good for saltwater tanks, some work better in freshwater ones. 

Internal Filters

You will find this filter in different styles. You simply have to put it in the fish tank or mount it to the side using suction cups. The air pump stays outside of the tank, while the airline should be connected to the filter inlet. Air is pumped into the filter’s bottom part and then expelled via the filter top.

Under Gravel Filters

An under-gravel filter uses a slotted base installed underneath the gravel. It comes with several uplift tubes to expand toward the water’s surface. To pull water through the gravel successfully, an air stone or a powerhead is installed in the tubes. 

When water flows through it, mechanical filtration media entraps the particles. To prevent deterioration, you must use a gravel cleaner to eliminate the particulates.

Sponge Filters

This one is attached to a tube from an air pump or powerhead. When water enters, the bacteria grow to build biological filtration. You can also use it for mechanical filtration, but it may get jammed due to excess detritus. As sponges can provide nitrifying bacteria, you can also use this filter for a hospital quarantine tank.

Keep in mind that such filters need cleaning with aquarium water. Tap water will kill all beneficial bacteria in the sponge. 

Trickle Filters

This filter exposes the water to the air as much as possible, thus fostering large groups of bacteria to break down waste. While these are famous for saltwater tanks, you can use them in freshwater tanks as well.

HOB Filter

A Hang-On-Back or HOB Filter is exactly what the name suggests, hanging on the back of the fish tank. These small-size filters are ideal for small to medium tanks. Their low flow rate is suitable for small tanks as high flow rates can damage the fish or plants. This one is adjustable and pretty easy to maintain.


There are some other filters like surface skimmers, sump filters, and UV sterilizers with some distinct characteristics. However, you have to learn about your fish tank and what type of filters will work best for them. 

Final Words

After going through our whole write-up on how does a canister filter work, things should be looking pretty clear to you now! And if you don’t know which one should you opt for, the Fluval 07 series canister filter can be an ideal choice for you to start. We also suggest you can go for OASE BioMaster Thermo 600. However, keep in mind, you have to properly take care of your aquarium regardless of what filter you are using.

The most important thing is to provide healthy and clean living conditions for those precious aquatic creatures. And at the end of the day, every filter type has its own advantages to offer you. While some may serve you on an average level, others would be generating more appealing outcomes. 

But remember, the most efficient ones often require more effort to keep them in good condition. While an aquarium canister filter may cost you extra cash and time, it’s definitely worth it! 

If You have any questions, please ask in the comments box, and we will be happy to answer.

Happy Aquarist! 

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