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20-Gallon Fish Tank Filter

Using a filter is important for maintaining good water quality in your tank. Without one, your aquarium will get dirty very quickly, affecting the health of your fish.

I’ve reviewed a list of products to give you a better idea of which 20-gallon fish tank filter is the best for you and your aquarium’s needs.

Review Summary

Best All-Rounder

MarineLand Penguin 100 Power Filter

It’s affordable, provides 3-stage filtration, and works very well. With a certified water flow rate of 100 GPH, this filter is more than powerful for a 20-gallon tank.

MarineLand Penguin 100 Power Filter

The best filter for the majority of 20-gallon tanks.

MarineLand’s Penguin 100 power filter is an excellent choice for most 20-gallon aquariums. Providing 3-stage filtration, this filter cleans your water effectively without costing an arm and a leg. It’s also simple to set-up and allows you to adjust the water flow rate.

Best on a Budget

Tetra Whisper In-Tank Filter

Tetra is a reliable and well-known brand in the fishkeeping community, so this filter is one you can trust. It’s an inexpensive option that also functions exceptionally well.

Tetra is a reliable and well-known brand in the fishkeeping community, so this filter is one you can trust. It’s an inexpensive option that also functions exceptionally well.

Tetra Whisper In-Tank Filter

The most affordable 20-gallon fish tank filter that also functions well.

The Tetra Whisper fish tank filter is a compact but powerful product. It’s inexpensive but cleans your aquarium to a high standard. This filter is easy to install, clean, and makes very little noise during operation.

Editor’s Choice

Fluval C2 Power Filter

The filter provides 5-stage filtration, which includes mechanical, chemical and two stages of biological filtration. This all helps keep your aquarium water crisp, clean and sparkling.

Fluval C2 Power Filter

My personal favorite 20-gallon aquarium filter. This filter is high-quality but a little costlier than the other products.

Although pricier than the other filters on this list, the Fluval C2 power filter is well worth its price-tag. It provides 5-stage filtration to keep your tank water crystal clear and comes with an adjustable water flow rate that doesn’t compromise filtration efficiency.

Types of Filters

Although you might not think it, there are a plethora of aquarium filters to choose from. They all essentially do the same job (i.e. provide filtration), but certain types are a better fit for specific set-ups and species of fish.

Undergravel Filters

As the name suggests, undergravel filters are placed underneath the substrate in your aquarium. They pull up the water via uplift tubes.

An undergravel filter is normally used with an airstone and air pump or a powerhead which is positioned over the top of the uplift tubes. 

NOTE

Using this type of filter can cause high levels of detritus and hydrogen sulfide to build up, so regular and thorough cleaning of your substrate is necessary.

Wet/Dry Filters

Also known as a trickle filter, a wet/dry filter is a popular choice in saltwater aquariums. They pump water from your tank through a drip plate or rotating spray arm before depositing it over biological material inside the filter chamber.

The water is then pushed back into your aquarium directly or through a sump. Wet/dry filters function best in setups with ample levels of aeration.

Opened Canister Filter
Opened Canister Filter

Canister Filters

A canister filter is commonly used in aquariums over 40 gallons, especially saltwater and planted setups. They can be quite expensive and are not necessary for tanks under 40 gallons.

Canister filters work by pulling water up through a lift tube and into an external filter chamber. The water is then pushed through filter media and distributed back into the tank. 

Internal Filters

For tanks under 20 gallons, internal filters are a good option. They need to be fully submerged in water to work. 

The base of the filter draws up water and passes it through a sponge that catches dirt and waste products. Beneficial bacteria thrive on this sponge and are crucial for converting toxic chemicals into less harmful forms.

Hang On Back/Power Filters

Hang on back/power filters are placed onto the back of your aquarium. They suck up water through a siphon tube.

Air-Driven/Sponge Filters

An air-driven/sponge filter is commonly used in breeding, hospital, invertebrate/small fish and nursery tanks. This type of filter does not offer a lot of chemical, biological, and mechanical filtration.

An air-driven/sponge filter is commonly used in breeding, hospital, invertebrate/small fish and nursery tanks…

Air-driven filters function with an air pump where water is drawn through a sponge-like material.

Which Type of Filter is Best for a 20-gallon?

The type of filter you use in your tank depends on personal preference and your aquarium’s needs, but for most 20-gallon aquariums, I advise using a power or internal filter. They’re affordable and easy to set up. They also provide a good amount of mechanical, chemical and biological filtration. 

3 Way Filtering Function 

There are three types of filtration: chemical, mechanical and biological. It’s a good idea to use all of them for your tank, but biological and mechanical are particularly important. 

Understanding Aquarium Filtration

Chemical Filtration

Chemical filtration uses activated carbon, resin, or other types of adsorbents to remove dissolved particulates from your aquarium. Using activated carbon in your tank is also useful for eliminating bad smells and soaking up medication.

Mechanical Filtration

Mechanical filtration strains particles like leftover food, debris, and fish waste from the water. This type of filtration is used with biological filtration to improve its efficiency. 

Biological Filtration

Beneficial bacteria is needed in every aquarium to convert ammonia into nitrite and nitrite into nitrate. This process is biological filtration. 

Fish Tank Inside a Dimly Lit Room
Fish Tank Inside a Dimly Lit Room

Which is Best for a 20-gallon Tank?

It’s best to have chemical, mechanical and biological filtration in a 20-gallon tank. However, biological and mechanical filtration are the most essential.

Water Flow Rate

No matter what type of filter you decide to use for your aquarium, it’s vital you pick one with a suitable water flow rate for the size of your tank. 

Your filter should be able to clean at least four times the capacity of your tank per hour…

Your filter should be able to clean at least four times the capacity of your tank per hour. For example, a 20-gallon tank requires a filter with a flow of at least 80 GPH (gallons per hour).

If you use a filter with an inappropriate water flow rate for your aquarium, then it can affect the quality of your water and the health of your fish.

Care of Aquarium Filter
Care of Aquarium Filter

Maintenance and Filter Media Replacement 

You need to look after your aquarium filter to keep it clean and working efficiently. Failing to do so will result in a dirty tank as your filter will struggle to clean the water.

It’s a good idea to check how well your filter is performing daily or during weekly water changes.

RECOMMENDATION

I recommend cleaning your filter and filter media every four weeks with water from your tank (don’t use tap water!). 

Most filter media does not need to be changed very regularly. How often you replace your media is open to interpretation, but most aquarists only change it when it is falling apart. Some fishkeepers replace it more frequently than this.

However, activated carbon loses its absorbency after around two to four weeks, so it will need to be replaced often. Additionally, filter floss needs replacing roughly every 5 days or when it is dirty.

Media like ceramic rings, plastic bio-balls, and coarse foams rarely need replacing unless they are heavily damaged. 

NOTE

When you decide to replace your biological filter media, make sure you seed the new bio-media for at least two weeks. Beneficial bacteria live on your filter media, so throwing it out without seeding the new one beforehand could cause your tank to crash.

20-gallon Fish Tank Filters Reviews

Best All-Rounder

MarineLand Penguin 100 Power Filter

It’s affordable, provides 3-stage filtration, and works very well. With a certified water flow rate of 100 GPH, this filter is more than powerful for a 20-gallon tank.

MarineLand Penguin 100 Power Filter

The MarineLand Penguin 100 power filter is my top pick for most 20-gallon aquariums as it’s affordable, provides 3-stage filtration, and works very well.

With a certified water flow rate of 100 GPH, this filter is more than powerful for a 20-gallon tank…

With a certified water flow rate of 100 GPH, this filter is more than powerful for a 20-gallon tank. It provides chemical, mechanical and biological filtration. As the filter uses cartridges, it is quite simple to maintain and clean.

I like the design of this filter as it’s fairly compact and looks attractive. Although visually appealing, the material can be a bit flimsy and some parts don’t fit together as well as they should.

Filter Media Basket

The filter media basket is a decent size to allow for extra biological material. Although not completely silent, the filter isn’t too loud as long as it’s well-maintained and your water level doesn’t drop past a certain point. However, the impeller can emit a grinding noise over time or if it’s not assembled properly.

Installing this power filter is relatively easy. Just follow the instructions provided to connect the parts, and then hang it on the back of your aquarium. 

TIP

You can alter the water flow rate by using the mid-level strainer, so it’s a good choice if you own fish that require a slower or faster current.

Specs

Pros

  • Compact and attractive design
  • Easy to install and clean
  • Decent size filter media basket
  • 3-stage filtration and adjustable water flow rate

Cons

  • Material is a bit flimsy
  • Can be a bit noisy

Best on a Budget

Tetra Whisper In-Tank Filter

Tetra is a reliable and well-known brand in the fishkeeping community, so this filter is one you can trust. It’s an inexpensive option that also functions exceptionally well.

Tetra Whisper In-Tank Filter

Tetra is a reliable and well-known brand in the fishkeeping community, so this filter is one you can trust. It’s an inexpensive option that also functions exceptionally well.

The filter uses Bio-Bag cartridges, so you don’t need to purchase additional filter media, which is convenient! 

Assembling the filter is pretty easy and doesn’t involve a lot of work…

Assembling the filter is pretty easy and doesn’t involve a lot of work. Just place the filter inside your tank using the two suction cups and you’re done! Cleaning the filter is equally as simple as the bottom of it can be removed to access the impeller inside.

Unfortunately, the clip/hanger and suction cups on the filter are a bit weak, so they may fall off easily and need reattaching regularly.

The Tetra Whisper filter is relatively silent, which is ideal if your aquarium is in your living room or bedroom. Internal filters are normally quiet, so you don’t need to worry about this one sounding like a jet engine!

Specs

Pros

  • Small size
  • Simple to install
  • Easy to clean
  • Quiet

Cons

  • Clip and suction cups aren’t very strong

Editor’s Choice

Fluval C2 Power Filter

The filter provides 5-stage filtration, which includes mechanical, chemical and two stages of biological filtration. This all helps keep your aquarium water crisp, clean and sparkling.

Fluval C2 Power Filter

Fluval is another popular manufacturer respected by aquarists, so their C2 power filter is one you can rely on. Out of all the products I’ve reviewed, this filter is my favorite as it looks great, offers ample filtration, and allows you to adjust the water flow rate.

The filter provides 5-stage filtration, which includes mechanical, chemical and two stages of biological filtration…

The filter provides 5-stage filtration, which includes mechanical, chemical and two stages of biological filtration. This all helps keep your aquarium water crisp, clean and sparkling. It can filter 119 GPH, which is more than enough for a 20-gallon tank.

Setting up and cleaning the Fluval C2 power filter isn’t too difficult, but it can be a little complicated if you’ve never used a power filter before. Unlike an internal filter, this power filter is placed on the back of your tank using the clip provided. 

Filter Maintenance

You need to clean the motor every three months for optimal performance. Unfortunately, this motor can be quite loud, which might be an issue if you’re looking for a silent aquarium filter.

You need to clean the motor every three months for optimal performance…

The impeller can also be a little fiddly to clean, but instructions do come with the filter to help you figure out how to assemble and clean everything. Maintaining the filter shouldn’t be too much of a challenge after the first couple of times. 

You get all the filter media you need to get your aquarium up and running, including a poly/foam pad, activated carbon insert, biological c-nodes, and biological bio-screen. I really like this as it means you don’t need to go out and purchase separate filter media. The filter media basket is also huge, which is a plus!

Another feature I like with this filter is that you change its flow rate without compromising filtration effectiveness. Decreasing the flow rate means that up to 50% of the filter inside the filter chamber is re-processed numerous times. This is ideal if you have fish or plants who prefer a slower flow but still need powerful filtration.

Specs

Pros

  • Provides 5-stage filtration
  • Adjustable water flow rate
  • Large filter media basket
  • Visually appealing

Cons

  • Can be a bit fiddly to assemble and clean
  • Can be quite loud during operation

Marina S20 Power Filter

Suitable for aquariums up to 20 gallons, the Marina S20 power filter cleans your tank effectively. The water flow rate can be adjusted, which is handy if you require a slower or faster current in your tank.

Marina S20 Power Filter

Suitable for aquariums up to 20 gallons, the Marina S20 power filter cleans your tank effectively. The water flow rate can be adjusted, which is handy if you require a slower or faster current in your tank. 

Installing the filter is straightforward as it is self-priming. Cleaning it is also simple.

This filter comes with four filter cartridges: two Bio-Carb and two Bio-Clear. Both of these cartridges contain Cermatiek, which is a very porous ceramic filter medium to allow for better biological filtration. There are a lot of extra compartments to allow for more filter media, too.

The design of the Marina S20 power filter is slim and compact to allow for more space in your aquarium…

The design of the Marina S20 power filter is slim and compact to allow for more space in your aquarium. One of my tanks uses an extremely bulky internal filter at the moment, so one this size is definitely something I’m in dire need of!

However, the filter can be a little loud at times, so this is something to keep in mind if your tank is located in your bedroom. 

Specs

  • Filter Type: Power
  • Size: 3.8” x 11.5” x 6.4”
  • Weight: 1.88 lbs
  • Recommended Tank Size: Up to 20 gallons

Pros

  • Simple to install and maintain
  • Adjustable water flow rate
  • Slim size
  • Extra compartments to allow for more filter media

Cons

  • Can be quite loud

Aqueon Quietflow E Internal Power Filter

With a water flow rate of 130 GPH, the Aqueon QuietFlow E internal filter provides your tank with good chemical, mechanical, and biological filtration. It includes a carbon cartridge, Bioholster, and coarse media sponge.

Aqueon Quietflow E Internal Power Filter

With a water flow rate of 130 GPH, the Aqueon QuietFlow E internal filter provides your tank with good chemical, mechanical, and biological filtration. It includes a carbon cartridge, Bioholster, and coarse media sponge.

the Aqueon QuietFlow E internal filter provides your tank with good chemical, mechanical, and biological filtration…

Cleaning and installing the filter doesn’t require much effort. Simply place the filter inside your tank using the provided suction cups and clips.

The filter doesn’t need priming and features at auto-start pump, which means it automatically turns back on during power interruptions. If you regularly encounter power cuts in your area, this internal filter might be a good fit for you!

The only things I don’t like with this filter is how open it is and its noisiness. I have a bristlenose pleco in one of my tanks who has a habit of climbing into small gaps, so I’d worry about him getting trapped inside this type of filter.

TIP

If you own small or curious species of fish, then this filter might not be the best match.

This filter isn’t deafeningly loud, but it still emits a fair amount of noise.

Specs

Pros

  • 3-stage filtration
  • Easy to clean and install
  • Features an auto-start pump

Cons

  • Open design might be problematic for some species of fish
  • Can be quite noisy

Penn Plax 455 Cascade Corner Filter

Capable of filtering 120 GPH, the Penn Plax 455 internal filter comes with one bio-sponge and one activated carbon cartridge.

Penn Plax 455 Cascade Corner Filter

Capable of filtering 120 GPH, the Penn Plax 455 internal filter comes with one bio-sponge and one activated carbon cartridge.

The feature I like the most about this filter is how slim it is, which means it very easy to hide. It can be placed horizontally in the corner of your aquarium using the included suction cups, making it simple to cover up with plants or décor.

You can adjust the water flow rate, as well as the direction of the flow spout…

You can adjust the water flow rate, as well as the direction of the flow spout. Additionally, this filter comes with a spray bar option to help distribute water evenly, thus adding more aeration to your aquarium.

Cleaning and installing the filter is easy, which is a plus! The only downsides with the Penn Plax 455 internal filter are its short lifespan and performance issues, especially in tanks with heavy bio-loads.

Specs

  • Filter Type: Internal
  • Size: 5” x 2” x 11”
  • Weight: 1.1 lbs
  • Recommended Tank Size: Up to 20 gallons

Pros

  • Slim, corner design
  • Adjustable water flow rate and direction
  • Comes with a spray bar option for even water distribution

Cons

  • Can sometimes have problems with performance
  • Not as long-lasting as other filters

Conclusion

Best All-Rounder

For most 20-gallon aquariums, I think the MarineLand Penguin 100 Power Filter is an excellent option. It’s affordable, compact, visually appealing, and offers good chemical, mechanical and biological filtration.

I like that you can adjust the water flow rate for a gentler or faster current, as well as add more filter media due to how large the media basket is. I also appreciate how easy the filter is to clean and install.

My main gripe with this filter is its flimsy material, which can make assembly a little fiddly. Additionally, the impeller can be a bit noisy during operation.

Best on a Budget

If you’re looking for an even cheaper aquarium filter, then the Tetra Whisper In-Tank Filter is another great choice. It’s the least expensive filter I’ve reviewed but also functions well and quietly.

Editor’s Choice

My personal favorite is the Fluval C2 Power Filter, which offers 5-stage filtration, an adjustable water flow rate, and attractive design.

However, any one of the other 20-gallon fish tank filters are worth taking a closer look if these three don’t appeal to you.

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