10 Best Filters for 20 Gallon Aquariums


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Aquariums are closed-off ecosystems that must be sustained through the efforts of the aquarist. In this respect, aquarium filters are a valuable tool for maintaining good water conditions in the tank.

The filter you choose for your aquarium must be rated for the water volume the tank can hold, and in this article, I will focus on the filters best suited for 20-gallon aquariums.

I’ll discuss 10 of the best filters for 20-gallon tanks along with their pros and cons, so you can choose the ideal filter for you.

What Type of Filter to Choose for 20 Gallon Fish Tank?

When it comes to medium-sized aquariums, there are a few filter options to consider:

Hang-on-Back Filter (HOB)

HOB filters are possibly your best choice when it comes to 20-gallon aquariums. These filters easily slide onto the edge of the aquarium, they’re easy to maintain, and offer mechanical and biochemical filtration.

They’re also affordable and silent as opposed to larger filter systems. What’s more, hang-on-back filters also efficiently filter the water volume they’re rated for.

Internal Filter

Internal filters are another option available for aquarium filtration, however, their efficiency is not comparable to that of HOB filters.

Internal filters are also more difficult to clean and maintain, but they can be a good option for small aquariums or terrariums where strong water flow is not needed.

Canister Filter

Canister filters are usually filtration powerhouses. They’re strong filters that can tackle the filtration of large aquariums. They sit outside of your aquarium, making a fair amount of noise compared to HOB filters.

For a 20-gallon tank, a canister filter may be an overkill. Canister filters are more suited for aquariums over 50 gallons, but you may find canister filters rated for smaller aquariums too.

Therefore, if you have a 20-gallon aquarium, a hang-on-back filter will be perfect for it. Simply choose a HOB filter that’s rated for 20 gallons. You’ll have the filter up and running in no time and it will be easier to maintain in the long run.

Choosing Filter for 20 Gallon Aquarium

Even if you’ve made up your mind about investing in a HOB, internal filter, or canister filter, you’re still going to have to make sure it’s correctly rated for your aquarium.

A good rule of thumb in choosing a filter size is that the water in your aquarium should pass through the filter four times per hour.

So, if you have a 20-gallon tank, you should get a filter that offers a flow rate of at least 80 gallons per hour.

If in doubt, always go for a bigger size. Undersizing your aquarium is not recommended and oversizing it is always a better option.

What you should be mindful of is that you may expose your fish to too much flow, but because some aquarium filters have built-in flow control mechanisms, you can easily choose a lower setting to accommodate the needs of your fish.

Best Filters for 20 Gallon Aquariums

Preview Filter Name  
1. AquaClear HOB Fish Tank Filter
2. GRECH CBG-800 Aquarium Filter
3. Fluval C Power Filter
4. Fluval Underwater Filter
5. MarineLand Magnum Canister Filter
6. Aqueon Quietflow Internal Power Filter
7. Fluval 106 External Filter
8. Penn Plax Cascade Canister Filter
9. Aqueon QuietFlow Canister Filter
10. Polar Aurora External Aquarium Filter

If you’re searching for best-in-line filters for your tank, here are my top picks for best filters for 20-gallon aquariums:

1. Aqua Clear – Fish Tank Filter

This HOB filter is a quiet and efficiently operating filter that I recommend for anyone looking for a power filter for their 20-gallon aquarium.

The filter media that comes with the Aqua Clear contains the AquaClear foam insert, the AquaClear activated carbon insert and the BioMax Ceramic rings for a 3-stage filtration process.

Because of its bottom-up design, this filter ensures that all your aquarium water goes through the filter bed, a system that reminds of the mode of operation specific to canister filters.

Another aspect that I find it’s worth mentioning about this HOB filter is the large filter container, which allows you to customize your own filter media should you wish so.

A further great feature of the Aqua Clear is its patented re-filtration system that enables you to control the flow rate and still achieve an up to 50% filtration of the water in the chamber multiple times.


  • Silent operation and durability
  • Possibility to customize filtration media
  • Mechanical and biochemical filtration
  • Adjustable flow rate
  • Easy installation


  • AquaClear filter media bags are slightly more expensive, but you can use your own media mix
  • Maintenance is required for propeller box as debris may get trapped


2. GRECH CBG-800 5W UV Sterilizer Hang-On Back Filter

This external HOB filter features a 5 W UV sterilizer that helps with the elimination of bacteria and algae, which is great if your fish aren’t otherwise algae eaters.

Besides the UV purifier, the Grech HOB filter also features bio media and activated carbon media, therefore, offering mechanical and biochemical filtration.

Another useful feature of this aquarium filter is its surface skimmer, which helps get rid of surface films.

In case you were wondering the UV sterilizer can be switched on/off independently, so if you don’t need to use it you can switch it off and turn it on when you do need it.

The flow rate is adjustable, and the compact design allows easy installation without the need of extra plumbing or tools.

I recommend this filter for anyone struggling with a tank prone to algae blooms as it’s very efficient at dealing with stubborn algae problems.


  • HOB with UV sterilizer for protection against algae and bacteria;
  • Adjustable flow and silent operation;
  • Easy installation;
  • Helpful surface skimmer;
  • Multi-stage filtration for a clean and clear aquarium.


  • Media basket design is a bit too tight;
  • Carbon filter that comes with it isn’t top quality, you may need to use your own.


3. Fluval C Power Filter

This is another HOB filter for 20-gallon aquariums that I insisted on including in this top 10 list of best aquarium filters because of its great value for money and has a 5-stage filtration.

This clip-on filter with modular media compartment allows you to clean each compartment one at a time. The media compartment is large and allows you to use your own media mix.

The Fluval C3 filter is rated for aquariums between 20 and 50 gallons. This filter also has a flow rate adjuster that allows you to reduce or customize the flow rate to required levels without compromising on filtration efficiency.

The 5 filtration stages can be broken down as follows:

  • Polyfoam media replaceable every 4-6 weeks;
  • Biological c-nodes replaceable every 6 months (only 50% of quantity, not all at once);
  • Activated carbon media replaceable every 2-4 weeks;
  • Bioscreen replaceable every 2-3 months;
  • Motor o-ring replaceable yearly.


  • 5-stage filtration;
  • Easy installation, assembly & disassembly;
  • Possibility to use own filter media mix;
  • Adjustable water flow.


  • Impeller is a bit difficult to clean;
  • Spout that trickles water on bio-media can clog up easily;
  • Filter replacement is easy, but you need to remember the different replacement dates that vary.


4. Fluval Underwater Filter

This internal filter from Fluval is rated for 20-40 gallon tanks. It installs easily and offers mechanical, chemical and biological filtration.

It can be mounted vertically or horizontally if water levels are lower, which is ideal for tanks with turtles that are filled only half-way because they feature a basking platform.

Because this is an underwater filter, filtration is carried out below the water level. Noise is minimal, only the silent hum of the impeller drawing water into the system.

Then there’s the option to set the flow output in 3 different positions to meet your specific needs:

If you want deep water agitation, you need to choose the Bottom Output setting. For a gentle and more even flow, choose the Spray Bar setting. The Top Output setting is for maximum circulation and oxygenation.


  • Multi-stage filtration;
  • 3-way flow control;
  • Vertical or horizontal installation;
  • Ideal for freshwater applications, reptile and marine environments;
  • Rated for 20-40 gallon aquariums.


  • Media compartment is a bit too small;
  • The U3 model may not be enough for a 40 gallon tank, which may better benefit from the U4 model.


5. MarineLand Magnum Polishing Internal Canister Filter

Designed to filter water in aquariums up to 97 gallons in size, this MarineLand canister filters is one of the better canister filters out there.

This is a strong filter that comes with 3-stage filtration, removing debris, toxins, colors, odours and more through chemical, mechanical and biological filtration.

The filter features a dual chamber for filter media, which allows you to make your own mix of filter media depending on your filtration requirements.

As an internal filter, the MarineLand canister filter is submersible, which means it will take up some space in your aquarium.

What’s great about it is that it’s self-priming, eliminating the need for manual priming. Cleaning is quite easy thanks to the easily removable lid.


  • Huge processing power (290 gallons/hour);
  • Ideal for large aquariums;
  • Offers all three types of filtration;
  • Customizable media because of large media chambers;
  • Easy to clean, self-priming.


  • Not compact, takes up a lot of space in the aquarium;
  • Fairly noisy;
  • Most suited for 50+ gallon aquariums.


6. Aqueon Quietflow Internal Power Filter

Ideal for aquarium or terrarium use, this Aqueon internal power filter offers three stages of filtration. It comes in different sizes, depending on how large your aquarium is.

The suction cups provided with the filter kit make it easy to install it. You can install it vertically or horizontally with adjustable return flow rate.

It’s a quiet filter, that’s submerged in water and requires no priming. Simply fix it in your aquarium with the suction cups, plug it in, and it’s all ready to go!

Cartridges in the Aqueon are easy to replace, there simply isn’t any hassle with maintenance, so you can add that to the list of advantages.

As for the filter media within the system, the Aqueon Quietflow contains a dense foam media for filtering out debris and particles, activated carbon media for chemical filtration, and a BioGrid for biological filtration.


  • Quiet and has good processing power;
  • Offers 3-stage filtration;
  • Cartridges can be easily changed;
  • Vertical or horizontal installation.


  • Takes up some space in the aquarium;
  • Smallest filter size lacks mechanical and biological filtration.


7. Fluval 106 External Filter

This Fluval external canister filter is rated for aquariums up to 25 gallons, therefore, if you’re looking for an external filter for your 20-gallon aquarium, this filter may be a great option for you.

Let’s see the features that make this canister filter a filter to consider for your freshwater or saltwater aquarium:

  • It offers multi-stage filtration, which is ensured by the twin foam pre-filters that clear your water of debris and prevent the clogging of other media, the two other chemical and biological filters;
  • Independent filter modules allow easy access to the media and easy changeover;
  • AquaStop valves ensure the interruption of water flow without leaks or disconnecting hoses;
  • Sound-dampened impeller for quiet operation;
  • Comes in four different sizes.


  • User-friendly canister filter with easy maintenance;
  • Multi-stage filtration;
  • Aquastop valves for hassle-free interventions;
  • Instant priming, no manual siphoning needed.


  • Powerful flow that needs to be mitigated with spray bar if low flow setting is required;
  • Impeller issues have been reported after 6-12 months, however, warranty is provided for 3 years.


8. Penn Plax Cascade Canister Aquarium Filter

This particular Recommended for aquariums up to 65 gallons, the Penn Plax Cascade canister filter offers 185 gallons per hour filtration. It’s available in larger sizes too for bigger aquariums, where more filtration power is required.

Start-up is made easy by the pushbutton primer, while the pool-style hose clamps make installation quick and hassle-free.

Flow rate can be adjusted with cut-off valves and the two media baskets can be customized as they’re spacious enough to fit your own filter media.

For a canister filter, it’s one of the quieter ones. If placed into a cabinet, you will not even hear it at all, which is great news for those with large aquariums.

Flow valves independently rotate 360 degrees for easy maneuvering. Spray bar and directional spout are both included with the filter kit.


  • Multi-stage filtration;
  • Easy set-up, comes pre-loaded with filter media;
  • Easy push button primer;
  • Adjustable flow rate;
  • Sturdy, tip-proof design;


  • Tubes can be a bit rough to connect;
  • Some priming issues were reported by users.


9. Aqueon QuietFlow Canister Filter

Providing a flow rate of 200 gallons per minute, this canister filter from Aqueon is designed for filtering water in saltwater or freshwater aquariums up to 55 gallons.

It comes preloaded with biological (Bio-Balls, Bio-Ceramic Rings), chemical (Activated Carbon) and mechanical (Coarse Foam) filter media for a thorough and complete filtration.

If the preloaded filter media combination is not what you need, you can customize it, and add your own media to the media chambers.

For those in need of a gentle flow, the spray bar is included with the filter kit along with two other attachments.

The filter is easy to set up and the included hang on the back water polishing unit makes maintenance quick and easy.


  • Flexible and easy setup
  • Multi-stage filtration
  • Quiet and functional unit
  • Easy access maintenance
  • Spray bar included


  • No issues were reported so far


10. Polar Aurora Free Media External Aquarium Filter

Even if you’re not familiar with canister filters, the user-friendly design makes this external aquarium filter a convenient choice even for beginners.

The Polar Aurora is rated for up to 75-gallon aquariums, offering a 3-stage filtration. The 3 media trays make it easy for you to pick your own choice of media and use that in the trays.

Canister filters always pack more power than their HOB counterparts, so for those needing a more gentle flow the Polar Aurora ships with an adjustable spray bar that allow easy adjustment of flow rates.

As with the other canister filters I reviewed in this article, the Polar Aurora is also a self-priming one, therefore, there is no need for manual siphoning.


  • Silent operation even if it’s a canister filter;
  • Self-priming, no manual siphoning needed
  • Can filter up to 265 gallons per hour
  • Useful surface skimmer
  • Possibility to use with own filter media


  • Newer model has no UV light (older models included a 9 W sterilizer lamp)
  • A fairly sizeable unit compared to HOB filters.



Even though I recommend a hang-on-back filter for most 20-gallon aquariums, there are quite a few canister filter and internal filters that you shouldn’t dismiss as an alternative to HOB filters.

As you can see, all filters have their pros and cons, but the filters I reviewed as best filters for 20 gallon tanks all have features that recommend them as a reliable choice.

All in all, the filter you choose should be able to efficiently filter the water volume in your tank and preferably offer 3 layers of filtration — mechanical, chemical and biological.

Noise levels and maintenance are other aspects to consider, but the filters I listed above are known for their quiet operation and ease of maintenance.

Updated: November 27, 2019

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