The Best Filter for Your 20-Gallon Aquarium

Alison Page

Alison Page


best filter for 20 gallon aquarium

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Whatever size aquarium you have, you need an efficient filtration system installed. Without a filter, the water in your fish tank will quickly become full of toxins that could harm or even kill your fish.

Read this guide to discover the best filter for a 20-gallon aquarium and more.

Quick Summary: Best Filter Systems for 20-Gallon Tanks

rc-table__imageAqueon Medium Filter Quietflow
  • Efficiently cleans and filters water
  • Easy to install using suction cups
  • Carbon Cartridge removes odors and discoloration from water
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Aqueon QuietFlow 10 LED PRO Aquarium Fish Tank Power Filter For Up to 20 Gallon AquariumsAqueon QuietFlow LED Pro Aquarium Power Filter
  • Easy To Use
  • Provides mechanical, chemical, biological and optional pad filtration
  • Self-priming filter pump
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rc-table__imageFluval 106 External Filter
  • Increased water filtration for cleaner, healthier water
  • 8-15% quieter than the Fluval 305
  • Easy to install and maintain
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Penn-Plax Cascade 500 Aquarium Canister Filter – Provides Physical, Biological, and Chemical...Penn Plax Cascade Canister Aquarium Filter 500
  • Compatible for both freshwater and saltwater fish tanks
  • Cycles water at 115 Gallons per Hour
  • Has 2 stackable, large capacity media baskets
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Tetra Whisper Power Filter for Aquariums, 3 Filters in 1, Up to 40-GallonsTetra Whisper Power Filter For Aquariums 3-in-1
  • Uses 3-stage filtration to create clear clean water
  • Ultra-Activated carbon removes both odor and water discoloration
  • Integrated Stay Clean technology
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Marina S20 Power FilterMarina Power Filter
  • Self priming
  • Easy to maintain
  • Adjustable flow control
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6 Best Filter Systems for 20-Gallon Aquariums

In this part of our guide, we review some of the best filtration systems for 20-gallon aquariums that you can buy on the current market.

Aqueon Medium Filter Quietflow

Aqueon filters are one of the best-selling brands on the market. The Aqueon Medium Filter Quietflow is a four-stage filter that includes biological filtration, mechanical filter, chemical, and stationary wet-dry filtration.

This high-quality system keeps your tank water crystal clear and healthy for your livestock, and the high flow rate ensures high levels of dissolved oxygen in the water.

The powerful filter pump is virtually silent and features an auto-restart following cleaning or power outages. You can use this filter system with saltwater aquariums and freshwater setups and it comes with a lifetime warranty.

What We Like:

  • Very quiet operation
  • Freshwater and saltwater compatible
  • Reliable and long-lasting
  • Lifetime guarantee

Room for Improvement:

  • Filter cartridges are pricey to replace

Aqueon QuietFlow LED Pro Aquarium Power Filter

Aqueon QuietFlow 10 LED PRO Aquarium Fish Tank Power Filter
  • LED indicator light flashes when water cannot pass through the cartridge, generally indicating it's time to change the cartridge
  • Self-priming filter pump will auto-start initially or restart if power is interrupted and restored
  • Provides mechanical, chemical, biological and optional, additional specialty pad filtration
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The Aqueon QuietFlow LED Pro Aquarium Power Filter is extremely well-made, almost silent, and super-reliable. 

The filter features an LED warning light that tells you when the filter cartridge requires replacement or cleaning, making it easy to keep on top of maintenance.

The pump is self-priming, so it’s simple to get the whole system up and running in no time. The powerful pump gives you a good flow rate, ensuring excellent oxygenation for healthy, lively fish.

This five-stage filtration system helps to keep your water clear and clean ensuring happy, healthy fish.

Phase one of the filtration system removes large particulate waste from the water, while stage two uses activated charcoal to remove chemicals and discoloration.

Stage three is a biological filter, stage four adds oxygen, and the final stage removes any residual contaminants, including phosphates.

What We Like:

  • Starts up automatically
  • 3-Stage Filtration
  • The internal pump helps dampen noise and eliminate leaks

Room for Improvement:

  • Poor durability

Fluval 106 External Filter

Fluval is a well-established company that has an excellent reputation for producing high-quality aquarium products at sensible prices, and its Fluval 106 Canister Filter is no exception. 

Thanks to the filter’s shape, this filter system offers a higher capacity than similar-sized units.

The filter box contains two media baskets, one for chemical filtration and one for biological filtration. This design also allows you to customize the system, as you can swap out the carbon for something else if you want to.

This filter provides an adjustable flow rate, which is an excellent feature if you keep fish that don’t like strong water movement. The system has an instant primer and includes special noise reduction technology, ensuring that the unit is almost silent and unobtrusive when in operation.

There’s an intake strainer and a mesh guard that prevent excessive amounts of debris from entering the filter. That makes the whole system more efficient and easier to maintain, too.

What We like:

  • Almost silent running
  • 3-stage filtration system
  • Hassle-free maintenance

Room for Improvement:

  • Quite pricey when compared to other filters

Penn Plax Cascade Canister Aquarium Filter 500

Penn-Plax Cascade 500 Aquarium Canister Filter – Provides Physical, Biological, and Chemical Filtration – 115 Gallons per Hour (GPH)
  • CASCADE 500 CANISTER FILTER: Without effort, the Cascade 500 Canister Filter quietly delivers crystal clear water throughout the tank. This filter cycles water at 115 Gallons per Hour, and is...
  • STATE OF THE ART FEATURES: In addition to the push button primer that allows for a simple and quick prime, this Canister Filter also features two independent valve taps that rotate 360°. This makes...
  • FILTER MEDIA: This Canister Filter comes standard with 2 Poly Fiber Floss Pads, 1 Coarse Bio-Sponge, and 1 Bag of Activated Carbon. In addition to optimizing the colonization of anaerobic bacteria,...
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The Penn Plax Cascade Canister Filter features two roomy, stackable filter media containers. You can use Cascade’s media, but that’s pricey, so we recommend using a cheaper alternative.

The water return mechanism is customizable, enabling you to choose the spray bar or regular return chute options, both of which are included with the filter system.

This external aquarium filter system does require priming before use, and there is a bit of preparation to be done before you’re up and running. You’ll notice a few air noises coming from the system while the air is expelled from the unit. That said, the system is pretty much silent once it’s working.

When it comes to maintenance, the system is simple to maintain. All you need to do is close the two water shut-off valves that connect to the hoses and take them off the top of the canister.

Lift the canister lid to access the media trays, rinse or replace the filter media, and put everything back together when you’re done.

What We Like:

  • Super-quiet running
  • Customizable filter media
  • Effective filter

Room for Improvement:

  • Filter media is quite expensive

Tetra Whisper Power Filter For Aquariums 3-in-1

Tetra Whisper Power Filter for Aquariums, 3 Filters in 1, Up to 40-Gallons
  • QUIET & RELIABLE The Tetra Whisper Power Filter uses 3-stage filtration to create clear clean water – PF 40 treats aquariums up to 40 gallons
  • ABSORBS ODORS Ultra-Activated carbon removes both odor and water discoloration
  • CATCHES DEBRIS Dense dual-sided mesh filters debris and fish waste
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Tetra Whisper 3-in-1 Power Filters are affordable filters that do the job without costing you a fortune.

The unit is sturdily constructed and is built to last. The flow rate is adjustable, and the spillway works well, agitating the water surface to provide your fish with plenty of dissolved oxygen.

The filter media that’s provided with the system isn’t very good quality, although it does provide lots of surface area for colonies of beneficial bacteria to grow and spread.

The pump is quiet, so there’s no annoying background humming sound to disturb you if you want to keep your aquarium in your office or bedroom. Also, this filtration system doesn’t contain any moving parts, so it’s less likely to fail. 

Overall, this filter system is easy to maintain, quiet, and well-made for its budget price.

What We Like:

  • Quiet running
  • Inexpensive to buy
  • Self-priming
  • Filter cartridges included

Room for Improvement:

  • Poor quality biological filter media

Marina Power Filter

Marina S20 Power Filter
  • Power filter for aquariums up to 20 gallons
  • Self priming
  • Easy to maintain
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The Marina Power Filter is a very neat unit that you clip to the back of your fish tank. The pump motor is installed inside the tank on the intake, while the filter media is housed in a clear plastic HOB unit.

Since the motor is already submerged, you don’t need to prime it every time it’s unplugged. The filter height is adjustable, enabling you to adjust it to suit different water levels, and the motor is extremely quiet.

You can adjust the flow rate and the strength of the current to suit your fish. Also, the flow rate is horizontal, so your fish won’t be pushed or buffeted around the tank, and that flow direction ensures good surface agitation for improved oxygenation.

The package includes four filter media cartridges; two Bio-Clear and two Bio-Carb that both contain Cermitek biological filter media.

What We Like:

  • Flow rate is adjustable
  • Easy to maintain
  • Super-quiet running 

Room for Improvement:

  • Flow rate could be more powerful

Different Types Of 20-Gallon Filtration Systems

Before we look at the different kinds of filter systems that you can buy, let’s talk about how a filtration system works.

The Parts of a Filtration System

There are three methods of water filtration:

  • Mechanical filtration
  • Chemical filtration
  • Biological filtration

Mechanical Filtration

The mechanical part of the filtration system is essential for aquariums of 20 gallons and over.

The filter pump pushes water through the unit with enough power to circulate that water right around the whole tank. As the water moves through the aquarium, it collects large waste particles and pulls them through the filter media, where it’s processed by beneficial bacteria.

Mechanical filtration also agitates the water surface, helping to oxygenate the water for your fish and counteract the effects of carbon dioxide.

When choosing a filtration system, you want one that provides a GPH (Gallons Per Hour) rate of at least four times that of the tank’s volume.

So, if you have a 20-gallon tank, you need a filter with a rating of at least 80 gallons per hour.

If the pump isn’t powerful enough for the size of the aquarium, the water won’t be circulated properly. This will result in dead spots in the tank and poor water conditions for the plants and fish.

Chemical Filtration

Chemical filtration uses activated carbon to remove harmful substances such as heavy metals and medication from the water.

Activated carbon is typically the chemical filtration element of choice and generally is what you’ll find contained in filter cartridges.

Biological Filtration

Biological filtration is just about the most important part of any filter system since it’s essential for the management of the Nitrogen Cycle.

The beneficial bacteria that live in your fish tank eat harmful toxins, including ammonia and nitrite, processing them into less dangerous nitrates. Nitrates can be used by your plants as a fertilizer, but you do need to remove excessive nitrates by carrying out partial water changes every week.

The biological element of a filtration system usually includes sponges or some other kind of media on which the colonies of bacteria can become established and grow.

Different Types Of Filters

There are several different types of filter systems that work well with a 20-gallon tank, including:

  • Hang-on-back (HOB) filters
  • Internal filters
  • Canister filters

Hang-on-back (HOB) Filters

HOB or hang-on-back filters are combination filtration systems that include mechanical, chemical, and biological filter elements in an enclosed box.

This kind of filter is sometimes also known as a “backpack” filter.

Internal Filters

As the name suggests, internal filters are housed inside the fish tank. This kind of filter comes in several different forms, including:

Box Filters

Box filters are the simplest design of an internal filter system and are generally the cheapest, making them a favorite choice of beginners to the hobby.

A box filter system is attached to the glass or acrylic viewing panes via suction cups.

Under Gravel Filters (UGF)

Under Gravel Filters or UGF, consist of a basic plastic plate that sits underneath the substrate.

An external pump is used to draw water through the substrate and up an outlet tower to be recirculated through the aquarium.

There is no filter media, and biological filtration takes place within the substrate and over the filter plate. 

This type of filter requires only annual maintenance when you have to take down the whole setup to clean out waste from underneath the plate.

UGFs tend to clog and don’t work well with plants, as the roots usually become tangled in the filter plate, making maintaining the system difficult. 

Canister Filters

Canister filters work well with a 20-gallon tank and are powerful enough to cope with high volumes of waste.

A canister filter unit lives outside the aquarium, usually concealed within a cabinet underneath the tank. 

What to Consider When Buying a Filter System for a 20-Gallon Tank

There are a few important factors to consider when choosing a filter system for a 20-gallon aquarium.


As mentioned earlier, a 20-gallon fish tank needs a filtration system that provides a GPH of at least 80 gallons. That will ensure that the flow through the aquarium is sufficient.

That said, you also need to take into account the shape of the aquarium when choosing a filter system.

For example, if you have a tall tank, an internal box filter will be too bulky, occupying the swimming space that your fish need and ruining the overall look of the tank.

So, if you have a tall tank, a HOB filter with a more compact design is a better choice.


The term “priming” refers to the process by which the filter is prepared for operation.

Typically, priming an aquarium filter entails filling the filter unit with water. If you fail to prime the unit properly, the filter will run with air in the pipework rather than water. This could cause the filter’s motor unit to burn out, the system will be extremely noisy, and the unit won’t circulate the water through your aquarium efficiently. 

Priming your filter system is not a big deal. However, if you don’t want the hassle of priming your filter, you should look for a self-priming or no-prime filter system.

These systems usually have a push-button primer that pulls the water through the unit’s pipework and into the holding tank, pushing out any air inside the pipes as it does so.

If you choose a system that needs priming, you simply fill the unit’s reservoir with water and then switch on the pump to draw water through the tubing. Your filter unit is then up and running.


Every filter system needs a degree of maintenance to keep it operating effectively.

The amount of maintenance required depends on the kind of filter system you’re running. However, the most common error made by newbies to the hobby is to clean the filter media too thoroughly or too often. 

Overzealous cleaning kills the beneficial bacteria that colonize the filter media, which could trigger the tank to recycle. 

Here’s a quick overview of the maintenance requirements of the most popular kinds of tank filters:

Hang-On-Back Filter

HOB filter systems generally require cleaning once a month or so, depending on how dirty your fish are.

You also need to change the filter media periodically, in line with the manufacturer’s guidelines.

Sponge Filter

Sponge filters are the simplest to maintain. All you need to do is take the sponge out of the filter box once a fortnight and rinse it in aquarium water to remove any excess sludge so that the sponge doesn’t get clogged up.

Canister Filter

Canister filters are pretty easy to maintain, only needing serious attention every three or four months.

Under-gravel Filter

UGFs are pretty much maintenance-free. All you need to do is vacuum your aquarium substrate every couple of weeks.

However, once a year, you do need to take down the tank completely so that you can give the plate a good clean.

Internal Filters

Internal filter units generally need cleaning around once a month. 

All you need to do is remove the filter media and rinse it in aquarium water, and wash away excess sludge from the impeller.

You will also need to replace the filter media periodically, depending on the brand of filtration system you choose.

Final Thoughts

Every fish tank needs an efficient, well-maintained filter system to keep the water clear and healthy for your fish. 

A 20-gallon aquarium needs a filtration system that provides a GPH rate of at least 80, but it’s up to you what style of filter you go for.

Canister filters perhaps have the lowest maintenance requirements and can be kept outside the tank, so you have an unobstructed view of your fish.

However, all the filters we’ve reviewed in this article are efficient, high-quality products that are well worth consideration.

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