Best Filter for a 20 Gallon Fish Tank

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The best way to keep your tank water in constant good health is by making sure that you buy the best filter for a 20 gallon fish tank that you can possibly buy.

Filters have the important task of removing waste and toxins from the water so that your fish can live a long and happy life.

There are different kinds of filters and each type has there strengths and weaknesses.

There are filters that are fully submerged inside your tank (Internal and sponge), others that hang on the back of the tank (HOB) and some that sit completely separate from your tank (Canister).

There are many excellent filters available so any of the ones I have listed below will be a good buy.

I do however have one favorite filter and that is the Fluval underwater filter 12 to 30 gallons. So, if you want to make a quick decision then this is the filter I would recommend that you buy.

It is quiet, very versatile and is great value for money. 

I have used way too many filters over my fish keeping time to remember every one of them but I am very happy with the filters I have chosen for your recommendation.

Here are my top choices:

Best Internal filter for 20 gallon tank 

I love internal filters. The reason why is because there is no danger of them leaking or overflowing and dripping water onto your floor.

If they do leak or overflow then the water just remains in the tank.

Internal filters are the most popular filters used in the fish keeping hobby.

They are also generally quiet to operate and they are self priming so if your power goes off and on again, your filter will just restart.

1) Fluval underwater filter 12 to 30 gallons – Top Pick

This is an outstanding filter made by one of the leading aquatic brands. 

The filter has 3 different ways that the water can flow. Water can flow from the top outlet, the bottom outlet or the vertically mounted spraybar situated between the two outlets.

A venturi (supplied) can be attached to the top outlet and both the top and bottom outlets can be directionally controlled.

Key Benefits:

  • Complete and efficient 3-stage filtration
  • Adjustable 3-Way Flow Control feature 
  • Can be used in fresh, marine or reptile environments
  • Flow rate of 105 GPH


  1. Very quiet 
  2. Directional and adjustable flow
  3. Top access for easy maintenance
  4. Can be placed horizontally as well as vertically


The venturi pipe is too short and does not stick out of the water if the filter is fully submerged 

The filter comes with Biomax biological media, 2 sponges and a combined polyester and carbon cartridge ensuring crystal clear water.

The media slides in and out on vertically mounted media trays.

2) Aqueon Quietflow E Internal Power Filter 

An economical and efficient internal power filter that can be used for both framed and frameless tanks.

You can attach the filter with suction cups or hang it inside the tank using the supplied clips.

This filter provides chemical, biological and mechanical filtration.

Key Benefits:

  • The filtration is chemical, biological and mechanical
  • It automatically restarts if power is interrupted and restored and does not need any priming
  • Install using suction cups and/or hanging clips
  • Flow rate of 130 GPH

Keep the water level even with the bottom of the outlet spout for the best water circulation.

A carbon cartridge (chemical filtration) helps to remove discoloration and odors from the water. While the bioholster (biological filtration) removes nitrites and toxic ammonia.

There is also coarse sponge media (mechanical filtration) that removes debris and particles for clearer water.


  1. Super quiet
  2. Primes itself when starting up
  3. Can install using clips or suction cups
  4. Agitates the water surface


  1. Takes up quite a bit of space
  2. Cannot adjust the flow rate

I recommend using the suction cups rather than the clips as we found this to provide quieter operation.

The Aqueon Quietflow E Internal Power Filter filter works efficiently and is very well priced. 

3) Whisper In-Tank Filter with BioScrubber for aquariums

A Whisper In-Tank Filter is convenient and quiet. It mounts on the inside of the tank which means that you can place your tank flush against a wall.

The motor of the filter sits under water which is way it is so quiet.

The Whisper In-Tank Filter offers the same quality and performance as an external filter.

It has the added bonus of functioning in as little as 2 inches of water making it ideal for turtle tanks.

You can adjust to high or low water levels using the mounting suction cups and/or the bracket.

Key Benefits:

  • The filtration is chemical, biological and mechanical
  • The filter does not need to be primed
  • Install using suction cups and/or hanging clips
  • Flow rate of 125 GPH
  • Can function in as little as 2 inches of water

Each filter comes with one pre-assembled Whisper Bio-Bag filter cartridge. I would suggest buying extra cartridges to make sure you have more on hand when needed.


  1. Space saving design
  2. Primes itself when starting up
  3. Install using clips or suction cups
  4. Agitates the water surface with it’s waterfall effect
  5. 2 Year limited warranty


Cannot adjust the flow rate

Warning – this filter is dangerous for betta fish. When they sleep then they can be sucked into the water intake. To avoid this happening, cover the water intake with either filter mesh or nylon silk stockings.

Make sure that the mesh or stocking is cleaned on a regular basis to avoid the filter not functioning correctly.

Best HOB filter for 20 gallon tank

Hang-on-the-back filters are also a great choice.

As the name implies, they hang on the outside of the tank and therefore do not take up any space inside the tank except for the water intake pipe.

HOB filters can normally hold a lot more filtration material then regular internal filters can.

1) Aqua Clear 30  HOB Filter

The Aqua Clear 30 HOB filter is suitable for fish tanks between 10 and 30 gallons.

This fish tank filter has the longest water to filter media contact and can accommodate 6 times the volume of filter media compared to similar sized filters.

Key Benefits:

  • The filtration is chemical, biological and mechanical
  • Adjustable water flow
  • Installation and maintenance is quick and easy
  • Flow rate of 150 GPH
  • Lifetime warranty


  1. Very reasonably priced
  2. Large filter media capacity
  3. Superior contact time with filter media
  4. Lifetime Guarantee on all non-replaceable parts


  1. There can be some vibration noise
  2.  Not advisable for tanks with sand substrate

The Aqua Clear 30 HOB filter comes equipped with AquaClear Foam, Activated Carbon Filter and BioMax and Cycle Guard for superior water quality.

Tip – Add 2 layers of poly-fil between the sponge and carbon media. This will make the water crystal clear and will not affect the PH levels. You can buy poly-fil at your local Wal-mart store.

2) Whisper IQ Power Filter for Aquariums, With Quiet Technology

The Tetra Whisper IQ Power Filter with Stay Clean technology keeps aquarium water clean and clear.

A soft barrier has been placed between the filter and motor which creates a sound shield to make this filter as quiet as possible.

Key Benefits:

  • Contains a sound shield for quiet filtration
  • Filter is self priming
  • Easy to use and easy to clean
  • Flow rate of 130 GPH
  • Flow rate can be reduced to as low as10 GPH for betta fish and planted tanks

The filter includes a bio-scrubber that cultivates aerobic bacteria which removes toxic ammonia and nitrites.


  1. Surface water is well agitated
  2. Adjustable flow
  3. Internal pump so no priming needed


  1. The filter is quite big
  2. Can overflow if the filter pads become clogged

Tip – To avoid the filter overflowing it is recommended that you cut about 3/8 inch off of the bottom of the plastic frame that holds the filter bag. This makes sure that the bag assembly sits lower in the body.

Make sure to adjust the flow if you have betta fish in the tank.

3) MarineLand Penguin Bio-Wheel Power Filter

All Penguin BIO-Wheel Power Filters deliver easy, three-stage mechanical, chemical and biological aquarium filtration. 

Within the Bio-Wheel is an indented wheel that turns and dips in and out of the water. This allows for the introduction of oxygen into the tank.

The Bio-Wheel provides excellent biological filtration removing toxins like ammonia and nitrite. It is covered by a  2-piece noise reducing vented cover.

The flow can be altered by adjusting the mid-level intake strainers.

Key Benefits:

  • Durable construction
  • Bio-Wheel gives excellent biological filtration
  • Easy to use and easy to clean
  • Flow rate of 150 GPH

The spacious interior of the filter allows it be easily customized to your liking. You can add bio-balls, filter floss or any other filter add-on’s.

If you are replacing an old filter then take some of the old filter’s media and place it in the new filter to help age the bio-filtration.


  1. 3-stage aquarium filtration
  2. Excellent bio-filtration
  3. Spacious and easily customizable interior
  4. Extremely durable
  5. Quiet operation


  1. Needs to be primed
  2. The Bio-Wheel can stop spinning if it becomes too dirty or the water level drops too much

Make sure that you stick to a regular maintenance schedule (once a week) with this filter to avoid the bio-wheel from stopping to spin. The water will quickly deteriorate if you do not pick up that the filter has stopped. 

4) Fluval C2 Power Filter

The Fluval Power Filter has an extensive five stage filtration system. This comprises of one chemical, two biological and two mechanical chambers.

The mechanical filtration traps large and fine debris while the biological filtration encourages good bacterial growth ensuring happy and healthy fish.

The chemical stage consists of activated carbon which helps to remove toxins from the water.

Key Benefits:

  • Extensive 5 stage filter
  • Cleaning indicator for when the polyfoam needs to be rinsed
  • Quick and easy maintenance
  • Flow rate of 115 GPH
  • Patented Re filtration System


  1. 5-stage aquarium filtration
  2. Flow rate can be reduced by up to 50%
  3. Quiet operation
  4. Ideal for heavily stocked tank
  5. Water flow adjustment


  1. Requires quite a bit of space behind the tank
  2. Some people had packaging issues

This is a powerful filter so if you have delicate fish like betta’s then insert a sponge at the end of the intake hose to avoid them being sucked in.

Best Canister Filter for 20 gallon tank 

Canister filters are the Rolls Royce of filters.

They sit outside your tank and consists of a large canister area with two hoses coming out the top. One hose draws the water out of the tank and the other hose returns the water to the tank via a spray bar or a spillway.

Canister filters do require more effort when installing, but they’ll keep your tank in far better condition than a power or HOB filter can. 

If you planning on heavily stocking your tank, having a planted tank or if you want goldfish then a canister filter is the way to go.

A canister filter comes with superior mechanical, chemical, and biological filtration capabilities. This type of filter is able to eliminate any kind of impurities inside the aquarium.

1) Fluval 207 Performance Canister Filter

The Fluval 207 Canister Filter comes with superior filtration abilities that make it suitable for all types of aquariums.

This seventh generation product has more than forty years of history and is noted as the best selling canister filter of all time.

Key Benefits:

  • Aquastop valves stop the water flowing without needing to disconnect hoses.
  • Energy-efficient
  • Powerful pump performance
  • EZ-Lift media baskets allow for easy media stack removal
  • Flow rate of 206 GPH
  • 3 Year limited warranty

This filter comes with 4 foam pads, 2 x 70g carbon, 2 x polishing pads, 2 x 120g BioMax, 2 x Bio-FoamAquaStop valve assembly, ribbed hosing, 2 rim connectors, intake tube, intake strainer, output nozzle, 2 rubber connectors, instruction manual and quick start manual.


  1. This filter is ultra quiet
  2. Single action dual Lift-Lock motor head clamps for quick release and attachment
  3. Fast, effortless start-ups with just a few pumps


  1. Needs to be set up below the level of the tank
  2. Tubing/fittings have a cheap feeling

The Fluval 207 Canister Filter’s extensive five stage filtration system is designed to create a healthy and clean environment for your fish.

This high level of filtration results in less maintenance being needed so you will have more time to just sit and enjoy your fish.

2) Penn Plax Cascade Canister Aquarium Filter

The Penn Plax Cascade Canister Filters are suitable for freshwater as well as salt water aquariums.

They offer heavy duty multistage filtration and can handle fish tanks up to 30 gallons in size. 

This canister filter is easy to install and it comes with everything that you need to get up and running very quickly. Flow rate control valves and swimming pool style hose clamps make setup and adjustment easy.

You should see a visible improvement in your tanks water in as little as a day.

The large filter trays allow you to really pack the media in. It can hold all 3 types of filtration media – biological, mechanical and chemical.

Key Benefits:

  • Quick release hose
  • 2 media trays
  • Flow valves that rotate 360 degrees for easy maneuvering
  • Push button primer
  • Flow rate of 115 GPH

The quick release hoses let you quickly disconnect hoses and keeps the water from draining out of the tank.

The flow valves (where the hoses connect) can rotate 360° so they can more easily fit under the tank stand at any angle needed.

The body of the canister is see through which makes it easier to see that it is filling up once you have primed the filter.

This filter comes with mechanical filter media and activated carbon, but it does not include any sort of bio-media. 


  1. Sturdy construction
  2. Casing is translucent so you can see how dirty the media is
  3. Easy setup
  4. Quiet Operation
  5. Flow can be adjusted


No biomedia included

The Penn Plax Cascade Canister Filter is a small filter that packs a whole lot of punch. It is perfectly suited to 20 gallon fish tanks.


I am quite comfortable with you choosing any of the filters that I have mentioned above.

I only recommend products that I like and that I have researched to see how other people have experienced them.

The filter is the most important piece of equipment you need to buy for your 20 gallon tank so make sure it is the best one that you can afford.

You can never over filter a tank so if in doubt always go bigger.

Photo of author


Irma Bense is the founder of She has over 42 years of experience in keeping fish.She has kept both freshwater and saltwater fish through the years.She has extensive knowledge in breeding numerous species of fish from Show Guppies, Cory Catfish, German Blue Rams to Apistogrammas.You can learn more about Irma on the 'About' page.