how do canister filters work

Generally, canister filters work in three steps. First, they draw water from the aquarium tank through the inlet tube. The water then passes through a series of filter media where debris, harmful chemicals and microorganisms are removed. Finally, the water is pushed back into the aquarium using a motor through the outlet tube.

We have prepared this article to provide you with the information you need to know about how canister filters work.

You may be interested in reading our separate article on best canister filters under $100.

What is a canister filter?

A canister filter is simply an external chamber (canister) that contains various filter media, a motor and tubes. 

Canister filters are used to screen out debris, harmful chemicals and microorganisms from the aquarium water. This leaves the aquarium water looking pristine thus providing a safe aquatic environment for your aquatic pets.

The external chamber is usually cylindrical and acts as the main chamber of the canister filter. The pump (motor) and filtering media (cartridges) are housed within the chamber. Attached to the external chamber are 2 tubes which act as an inlet and outlet tube.

You can use the filter by placing the chamber outside the aquarium. However, you can submerge some models such as the MarineLand Magnum Internal Polishing filter inside the aquarium.

How do canister filters work?

Canister filters operate through the principle of siphoning water. The water is siphoned out of the aquarium using an inlet and back using an outlet.

Siphoning is the process of creating an uninterrupted flow of water between 2 water bodies. This principle enables water to flow freely without the need of a pump.

To work effectively, canister filters use three main components namely.

  1. Inlet and outlet tubes
  2. Cartridges that hold the filtration media
  3. Motor (pump)

To enable you to understand how canister filters work, we will look at the function of each component separately.

1.      Inlet and outlet tubes

The inlet tubes and outlet tubes connects the canister filter to the aquarium tank. These tubes are usually made of vinyl depending on the brand of the filter.

The inlet tube allows water to flow into the canister filter from the aquarium tank. The outlet tube on the other hand, allows water to flow back into the aquarium tank.

The tubes are usually adjustable in most canister filters.

Additionally, depending on the brand of the canister filter, they may offer multiple options on how water flows in and out of the tank. The options include a spray bar, jet return or lily pipe, among others.

2.      Cartridges and filtration media

Inside each canister filter is a series of filter cartridges. The number of filter cartridges varies from one filter to another depending on the brand and model of the canister filter.

Some manufacturers used media trays while others use filter cartridges. The filter cartridges (media tray) performs one of three highly important functions. These however depends on the type of filter media it holds.

In some models, you can choose the type of filter media you want to use on your aquarium depending on your aquarium needs.

Mechanical filtration

Mechanical filtration is the process by which a canister filter removes debris and solid waste materials from aquarium water.

Canister filters contain a form of filter media that act as a strainer. The strainer removes free floating solid particles through the process of mechanical filtration.

Depending on the brand of canister filter you are using, the strainer can either be a filter floss, special filter pads, sponge or aquarium gravel.

Chemical filtration

Chemical filtration is the process by which chemical additives are used to remove dissolved wastes from aquatic water. Canister filters include chemical additives in their filtration system that perform this function.

Common chemical additives used include activated charcoal, purigen or other chemical resins.

The type of chemical additive used will depend on the specific brand of canister filter you are using. Some canister filters are flexible such that they may allow you to choose your preferred type of chemical additive.

Biological filtration

Biological filtration is the process by which bacteria and other microorganisms convert your fishes’ wastes into less toxic substances.

Aquarium fish excrete waste into the aquarium constantly as they utilize the food they eat. This waste (ammonia and nitrites) is potentially toxic to fish. It causes several health problems to fish.

A biological filter converts toxic ammonia into nitrites, and toxic nitrites into nitrates.

Canister filters provide for biological filtration by providing a large surface area for growth of beneficial bacteria. The bacteria then convert the toxic waste into less toxic substances.

To provide for biological filtration, manufacturers use several different types of filter media. Most canister filters use filter media such as ceramic rings or bio rings.

3.      Motor

Either an internal motor or an in-tank pump powers a canister filter. The motor forces water into the canister. Once filled with water, the internal pump then powers the filter. The internal pump forces water out of the filter back to the aquarium tank through the filter’s outlet tube.

The location of the internal motor varies with the manufacturer. Internal motors are either built into the cover or the base of the canister filter. However, they work in the same way basically.

Internal motors eliminate the need for an external pump. External pumps take up space within the tank. Furthermore you can easily clean an internal motor when servicing the filter. Therefore internal motors are more advantageous.

Canisters with internal pumps operate at specific pump flow rates. Check with the manufacturer of your cannister filter for the flow rate of your pump.

How does water pass through the filtration media?

Water passes through the filtration media in a systematic manner.

First, a motor forces water from the aquarium tank into the canister through an inlet tube. The motor forces water into the canister by creating a suction force.

Once inside the canister, the water passes through a system of filter media. The filter media screens and cleans the water.

Lastly, the motor then forces the clean water back to the aquarium tank through the canister’s outlet tube.

The water flow within the canister varies depending on the brand and model of the canister filter. The direction of water flow can be either of the following.

  • Top to bottom
  • Bottom to top
  • Back to front
  • Center out
  • Center in

Different manufacturers have different preferences. Whatever the direction, the end result is usually the same. The aquarium water passes through a series of filter media which screens and cleans the water. Choose a canister filter depending on your aquarium needs.

FAQs about how canister filters work

How effective is a canister filter?

Canister filters are very effective filters if used and maintained correctly. There are several reasons why canister filters are effective.

Firstly, depending on the model of canister filter you are using, canister filters filter the aquarium water several times in an hour unlike other types of filters. This leaves the water looking pristine and provides a safe aquatic environment for your fish. Furthermore, in most canister filters you can adjust the flow rate of the filter making canister filters not only effective but versatile as well.

Secondly, canister filters are easy to install and use unlike other filters.

Additionally, canister filters are very effective because they allow for mechanical, chemical and biological filtration of the aquarium water. However, this depends on the filtration media you are using in the filter. In most canister filters, you can choose the type of media you want to use depending on your aquarium needs.

In addition, canister filters operate quietly unlike other types of filters. Therefore your aquarium fish will not undergo the stress caused by the noise produced when the filter is in operation and thus will thrive.

Lastly, canister filters do not take up a lot of space in the aquarium. Most canister filters are placed outside the aquarium however some brands are submerged in the water.

What are the benefits of a canister filter?

Canister filters are preferred over other type of filters because they have many benefits.

First, canister filters are versatile. You can use a canister filter on different types of aquarium set ups. You can use canister filters to clean both freshwater and saltwater tanks. Additionally, you can use a canister filter even on a turtle tank that usually has a lot of mess. Furthermore, you can use a canister filter for different purposes provided you clean and maintain it correctly.

Secondly, canister filters are very effective. They allow for efficient mechanical, chemical and biological filtration. This leaves the aquarium water looking pristine and safe for your fish. Furthermore, in most canister filters you can choose the type of filter media to use allowing you to determine the level of filtration you require in your tank.

Additionally, canister filters operate quietly. This provides a stress free environment for your fish and reduces the noise created by other filters in your house.

In addition, canister filters are very powerful. They can filter the aquarium water several times in an hour. This ensures that the aquarium water is clean and safe for your fish. Furthermore, in most canister filters, you can adjust the flow rate of the filter. This allows you to determine the number of times the water is filtered depending on your aquarium needs.

Lastly, canister filters are easy to install and use. Canister filters are designed in a way that you can easily disassemble and reassemble them for maintenance. This makes canister filters easier to use unlike other type of filters.

Read next: Best filter for axolotl tank.

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