Best Filters For 20 Gallon Aquariums – Reviews & Guides

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There are many filter types which you can choose for a 20 gallon fish tank. They include power, canister, and internal filters. These are the most popular and powerful types of aquarium filters today. If you are a beginner and don’t have any experience with any type of aquarium filters, read the complete aquarium filter guide here. If you’ve already had some basic knowledge about the fundamental of aquarium filters and are finding the best filter for your 20 gallon aquarium, this article is for you.

Top Filters for up to 20 Gallon 

Great flexibility - Editors choice
  • Quick And Easy Installation
  • Easy To Clean And Maintain
  • Awesome Filter With Great Flexibility
  • Quiet And Effective
efficient filter - Best value
  • Easy To Customize
  • Quiet And Efficient
  • Easy To Use
  • Easy To Change Cartridge
Crystal Clear Water - High Quality
  • Customizable
  • Quality Design And Easy Maintainance
  • Extremely Quiet
  • Crystal Clear Water
Excellent Water Cleaning - Great Value
  • Great For Pet Water Fountains
  • Great Silent Filter
  • Quiet And Super Effective
  • Excellent Water Clearing
Reliable And Quiet - Best Quality
  • Good Features And Clears Water
  • Functional And Quiet
  • Reliable Easy Set-Up
  • Great Quality
Exceptional Filter - Highly Recommended
  • Easy Set-Up
  • Quiet Operation
  • Quality Build And Powerful


  • TypePower Filter (Hang-On-Back)
  • Flow Rate: 100 GPH (Gallons Per Hour), Adjustable
  • For Tank Sizes: 5 To 20 US Gallons
  • Filtration Types: All 3 Types Of Filtration
  • Filter Media: AquaClear Foam, Activated Carbon, BioMax Ceramic Rings.

The AquaClear 20 power filter features a larger media capacity compared to other comparable filters that are rated for the same tank sizes. With the large filtration capacity, the filter is very flexible to use filter media that makes it the most favorite filter on the market. You can choose your own filter materials to work with the filter and don’t have to use ones from the manufacturer.

It comes with some filter materials like AquaClear foam, activated carbon and BioMax that are necessary for setting up a complete system with mechanical, biological, and chemical filtration. With the grid of all types of filtration provided, the filter ensures that all the water going through it is properly filtered and safe for the fish to live in.

People love to use the filter with only biological and mechanical filter media to provide the ultra-clean environment for their fish; and they only add activated carbon media to perform the chemical filtration when the aquarium water looks yellowish.


Cycle Guard with BioMax. Source:

The filter is very popular on the aquarium hobby and its quality is proven by thousands of hobbyists on the world. With its very affordable price, quality and customization ability, I strongly recommend this filter for creative hobbyists who want to build their own filtration system. This is also the best 20 gallon aquarium filter in this review.

  • Quality product keeps the water clean and clear,
  • Large filter capacity to contain more filter media,
  • Very flexible to use filter materials,
  • Very quiet,
  • The flow rate can be adjusted without changing its efficiency,
  • Easy to set up and maintain,
  • Cheap to maintain,
  • Impeller can be easily replaced,
  • 2 year warranty.
  • the only drawback is its little expensive price.

Pro Tip

The filter features a flow rate of 100 gallons per hour which is strong enough to keep a tank with 20 gallons of water clean and clear for a long period. The flow rate can be adjustable to fit various tank sizes and fish types, so don’t worry if it is too strong for your tank.

The flow rate can be reduced up to 50% without interfering with its filtration efficiency because of its patented re-filtration system (Cycle Guard with BioMax). This system holds the water within it for processing multiple times when the flow rate is reduced.


  • Type: Power Filter
  • Flow Rate: 92 GPH, Adjustable
  • Rated For: Up To 20 US Gallons
  • Filtration Types: All 3 Types Of Filtration
  • Filter Cartridges: 2 Bio-Carb (Activated Carbon And Ceramic), 2 Bio-Clear (Zeolite And Ceramic).

I like Marina because of their quality aquarium kits like the Marina LED aquarium kits for starters. Their quality products have satisfied most customers from the new comers to advanced hobbyists. You can easily notice that when you read the reviews of Marina’s products.

The only drawback of this filter is its capacity smaller than the Aquaclear 20 and you have to buy the filter cartridges for the maintenance. However, the abundance of biological filter materials (zeolite and Ceramic) included in the filter cartridges ensure that harmful nitrogenous toxins (ammonia and nitrite) are degraded and no longer harm your aquarium inhabitants. So, it is worth for your money.

  • Compact design,
  • Quality product keeps the water clean and clear,
  • Quality cartridges excellently perform biological filtration,
  • Can adjust its flow rate,
  • Easy to set up and maintain,
  • Very quiet operation.
  • Less filter capacity than AquaClear power filters,
  • have to use the cartridges from the manufacturers,
  • High operation cost for buying cartridges.

Pro Tip

Marina Slim S20 power filter features a very compact design for easy setup, even in small spaces. It features an adjustable flow control that makes it an ideal choice for small tanks up to 20 gallons.

The best feature of Marina Slim S20 power filter is that it operates so quietly but still ensures its filtration efficiency. It can start itself after installation, cleaning or power interruptions without the need of manual priming.


  • Type: Power Filter
  • Flow Rate (Gallon Per Hour): 119 GPH, Adjustable
  • Ideal For: 20-25 US Gallon Tanks
  • Filtration Types: 5-Stage
  • Media: Fluval C2 Poly/Foam, Activated Carbon, C-Nodes And Bio-Screen (Drip Tray Pad).

This is a high-quality power filter manufactured by Hagen Fluval, a well-known brand for their aquarium products. The product includes everything you need to get started: activated Carbon for chemical filtration, C-nodes for the colonization of helpful bacteria (biological filtration), and foam pad for mechanically filtering solid particles in aquarium water.


5-stage filtration, image from Fluval Aquatic

The special feature of this filter is its 5-stage filtration that really make your aquarium water clean and clear, and provide a healthy environment for your fish to live in. These include:

  • Stage 1 & 2: poly/foam pad mechanically removes waste particles out of the water.

  • Stage 3: activated carbon insert removes heavy metals, odors and discolorations to keep the water clear.

  • Stage 4: Bio-Screen (a drip tray pad) trickles the water and make it well aerated and ready for biological filtration stage.

  • Stage 5: C-Nodes provides optimal living space for helpful nitrifying bacteria, which processes nitrogenous toxins (ammonia and nitrite).
  • Good idea of 5-stage filtration,
  • Quality product keeps the water clean and clear,
  • Can adjust its flow rate,
  • Free to use filter media,
  • Easy to set up and maintain,
  • Very quiet operation.
  • A little expensive,
  • Less filtration capacity than AquaClear power filters.


  • TypeInternal Filter
  • Flow Rate (Gallon Per Hour): 125 GPH
  • For Tank Sizes: 10-20 Gallons
  • Cartridge: One Pre-Assembled Whisper Bio-Bag Filter Cartridge.

This is an internal filter (or internal power filter) which is placed and works inside the aquarium. The internal filter is the most traditional type of aquarium filters and very familiar with even beginners. This in-tank filter is compact, cheap, easy to install and use. Only assemble the filter, then position it inside your aquarium (submerge into the water), and the filter will do its work to keep the tank clean and clear.


Bio-scrubber for biological filtration

The filter uses a medium Whisper bio-bag cartridge and a patented Bio-scrubber pad to provide a three-stage filtration. The Whisper bio-bag cartridge is a floss pad filled with activated carbon to eliminate waste particles, odors, and discolorations in the aquarium water. The Bio-scrubber pad provides a large surface for helpful bacteria to thrive in.

  • Dirt cheap,
  • Bio-scrubber for biological filtration,
  • Almost no noise while operating because it is submerge in the water,
  • Ideal for low-level water tanks, turtle tanks.
  • Take space inside the aquarium,
  • Less media capacity than power and canister filters,
  • The biological stage seems so weak,
  • Can’t adjust its flow rate,
  • Have to use the cartridge from the manufacturer.

If you love to use internal filters, this one is designed for you.


  • TypeCanister Filter
  • Flow Rate (Gallon Per Hour): 145 GPH, Adjustable
  • For Tank Sizes: Up To 25 US Gallons, Both Fresh And Saltwater
  • Filtration: 3 Types Of Filtration
  • Media: 4 Foam Pads, 1 X 70 G Carbon, 1 X 120 G BioMax
  • Number Of Baskets: 2 Media Baskets
  • Warranty: 3 Years.

Most aquarists prefer to filter their fish tanks with canister filters despite the fact that they are usually much more expensive than power or internal filters. Although this type of aquarium filters is commonly designed for medium to extra large aquariums, there are a few ones rated for small tanks under 20 gallons and the Fluval 106 canister filter belongs to this group.

filtermedia 106

Fluval 306 filtration system, source Fluval Aquatic. (1) vertical large foams,
(2) Bio-foam, (3) BioMax ceramic rings, (4) Fluval Carbon

The filter chamber of the Fluval 106 is larger than other comparable canister filters that are rated for the same tank sizes. It includes two large filter media baskets that is capable of accommodating a variety of filter media. Because its capacity is much bigger than other filters, it has the advantage of containing more filter materials for better filtration and less maintenance (longer periods between maintenance times).

The filter is rated for aquariums up to 25 gallons and certainly it is the best choice for a 20 gallon aquarium if you are considering a canister filter.

  • Excellent performance of three types of filtration,
  • Large capacity, 35-50% more than round canisters,
  • Convoluted water flow pattern for better water-media contact,
  • High and adjustable flow rate,
  • Sound dampening impeller for quiet operation,
  • Instant priming by pressing the button on the lid,
  • Easy to disassemble for maintenance,
  • Large capacity for low maintenance
  • Easy to find replacements,
  • 3 year warranty.
  • More expensive than other filters.

Read the full review of Fluval 106 canister filter:


  • Type: Canister Filter
  • Flow Rate (Gallon Per Hour): 115 GPH, Adjustable
  • Ideal For: A 20-25 Gallon Aquarium, Both Marine Or Freshwater
  • Filtration Types: All 3 Types Of Filtration
  • Filter Media: Bio-Floss, Bio-Sponges, Activated Carbon.

This is also a small and compact canister filter for medium tank size up to 25 gallons. The filter features multiple removable filtration chambers to contain any filter material you want. It also come with some filter media such as bio-floss, bio-sponges, activated carbon to perform multi-stage filtration and completely purify your aquarium water.

The Cascade 500 canister filter is very easy to set up and maintain. Once installed, the filter works fast to keep your aquarium clean and clear. It takes you about thirty minutes for installing the product and you can notice the improvements of your aquarium after only a day.

  • Very affordable price for a canister filter,
  • Large capacity for excellent performance of three types of filtration,
  • High and adjustable flow rate,
  • Quick and easy to prime by pushing the button on its top,
  • Flow rate control valves and easy-lift clamps for easy setup and maintenance.
  • Less durable than Fluval 06 series canister filters.

Top Editor's Choice on 20 Gallon Fish Tank Filter

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