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Best Filter For 20 Gallon Tank – Picks For Strong Filtration

It doesn’t matter if you have a small fish tank or a super-size setup, if you don’t install an efficient filtration system in your aquarium, the water will quickly accumulate harmful toxins that could kill your fish. Have you heard of the “Nitrogen Cycle?” That’s a must-know for all fish keepers, as, if you don’t manage the Nitrogen Cycle in your tank properly, you could end up with a tank full of sick or dying fish.

In this guide, we look at the best filter for a 20-gallon tank, including detailed reviews of our recommended filtration systems to help you make the right choice for a clean tank and healthy, thriving livestock.

Quick Comparisons of the 7 Best Filters For 20-Gallon Tanks

IMAGE BRAND DETAILS
tnk-table__imageAquaClear Power Filter
  • HOB Filter
  • 100 GPH
  • AquaClear Foam, Activated Carbon and BioMax
View Product
tnk-table__imageAqueon Medium Filter Quietflow Internal, 20-Gallon
  • Internal Filter
  • 130 GPH
  • Filter cartridge, Sponge, Biological
View Product
tnk-table__imageAqueon QuietFlow LED Pro Aquarium Power Filter
  • Internal Filter
  • 100 GPH
  • 5-stage multi-media filter system
View Product
tnk-table__imageFluval 106 External Filter
  • External Filter
  • 145 GPH
  • 3-stage filtration system
View Product
tnk-table__imagePenn Plax Cascade Canister Filter 500
  • Canister Filter
  • 115 GPH
  • 3-stage filtration system
View Product
tnk-table__imageTetra Whisper Power Filter For Aquariums 3 in 1
  • HOB Filter
  • 210 GPH
  • 3-stage filtration system
View Product
tnk-table__imageMarina Power Filter
  • HOB Filter
  • 92 GPH
  • 3-stage filtration system
View Product

Different Types of 20-Gallon Filters

There are a variety of different filter systems, and we’ll look at those in more detail below. But first, let’s discuss how filtration systems work.

Elements of a Filtration System

The three methods of water filtration are:

  • Biological filtration
  • Chemical filtration
  • Mechanical filtration

Sponge aquarium filter icon. Isometric of sponge aquarium filter vector icon for web design isolated on white background

Biological Filtratio

Biological filtration is arguably the most important part of any filtration system for any size of a tank, as it manages the Nitrogen Cycle. Beneficial bacteria in your aquarium consume ammonia and nitrites, breaking them down into less harmful nitrates. Nitrates are utilized by live plants as fertilizer, and any excess is removed each week via partial water changes.

The biological element of a filter usually consists of sponges or other media on which colonies of bacteria can grow.

Chemical Filtration

Chemical filtration uses activated carbon to get rid of substances such as medication and heavy metals from the water. Activated carbon is usually the go-to chemical filtration element of a system and is generally contained in filter cartridges.

Mechanical Filtration

The mechanical element of a filter system is crucial in tanks of 20 gallons and larger. A pump pushes the water through the filter unit with sufficient power to circulate the water through the whole aquarium, picking up particulate waste and drawing it through the filter media where beneficial bacteria process it.

Mechanical filtration also helps to aerate the water, helping to counteract the negative effects of carbon dioxide and keeping the environment well-oxygenated for your fish.

An efficient and effective pump circulates water around the aquarium at least four times every hour. So, for a 20-gallon fish tank, you need a filtration system with a GPH (Gallons Per Hour) rating of at least 80 GPH, preferably more. If the pump isn’t powerful enough for the size of the tank, the water won’t circulate properly, resulting in stagnant spots in your aquarium and poor conditions for your fish and plants.

Types of Filters

The most popular types of filtration systems are:

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

Hang-On-Back (HOB) Filters

Aqueon QuietFlow LED Pro Aquarium Power Filter

Hang-on-back (HOB) filters are combination filtration systems that contain biological, mechanical, and chemical elements in an enclosed case, hence their other name, backpack filters.

Internal Filters

Aqueon Medium Filter Quietflow Internal

Internal filters come in several different styles and are suitable for use with 20-gallon aquariums. As the name suggests, internal filters are fitted inside the aquarium.

Box filters are the most basic design of the internal filter system and are often the most reasonably priced, making them a popular choice for newbies to the hobby. Box filters fix to the tank glass via suckers.

Under Gravel Filters (UGF) are an internal filtration system that consists of a simple plastic plate that is fitted underneath the substrate.

UGFs also clog and are not the best choice for planted tanks, as plant roots can become enmeshed in the filter plate, making maintenance tricky.

Canister Filters

Fluval 106 External Canister Filters

Canister filters are a good choice for a 20-gallon tank, and they are also powerful enough to cater to dirty species of fish, such as goldfish. Canister units are placed outside the tank, often hidden underneath the aquarium in the cabinet.

Benefits of Using a Filter For A 20-Gallon Aquarium

A 20-gallon or 25-gallon aquarium is a very popular tank size for beginners, as it’s big enough to create an interesting and impressive display of fish and plants, but not so large that maintenance is unduly time-consuming. That said, a 20-gallon tank won’t remain a clean and healthy environment for your fish if it doesn’t have an efficient filter system.

There are several important benefits for using a filter system with a fish tank of that size:

Water Quality

All living creatures, including fish, invertebrates, and mollusks, produce waste products. Over time, that waste decomposes, creating harmful toxins that pollute your tank water. Without an efficient filter system, your aquarium environment will quickly become a toxic soup that poisons the fish and other tank inhabitants.

How The Nitrogen Cycle Works - Aquarium with small fishes and a beautiful aquascape.

Although you can dilute the levels of waste in the water by carrying out weekly partial water changes, a biological filtration system controls and manages the Nitrogen Cycle, removing ammonia and nitrites from the water and converting them to less dangerous nitrates. Plants utilize nitrates as a fertilizer, helping to remove some of these compounds from the water, and your regular partial water changes will take care of the remainder. Ideally, the nitrate level in your tank should be below 20 ppm, while ammonia and nitrite levels should be zero.

Water Oxygenation

Fish need oxygen, which they extract from the water through their gills, expiring carbon dioxide as they breathe. Living plants absorb carbon dioxide from the water during photosynthesis and expire oxygen back into the water. That sounds great, but many fish species require well-oxygenated water to thrive, and a powerful mechanical filtration system helps to provide the fish with the extra oxygen they need by pushing air bubbles into the water and agitating the water surface.

Tank Maintenance

Cleaning the aquarium. Pumping water out of the aquarium. Close-up. Siphon Gravel Cleaner Tool In The Aquarium. Aquarium fish content and hygiene concept.

You should vacuum your aquarium gravel as part of your weekly maintenance regimen. However, an efficient filtration system can help to lighten your workload by removing much of the floating particulate and detritus that would otherwise find its way into the substrate. For that reason, you will need to rinse the filter media in tank water every month or so to get rid of excess sludge that would otherwise clog the system.

Factors to Consider When Buying a Filter For A 20-Gallon Tank

There are several important considerations to make when choosing a filter for a 20-gallon aquarium.

Size

For a 20-gallon aquarium, you need a filtration unit that has a GPH rating of at least 80 gallons. That ensures that the water flow around the tank is adequate. However, the shape of the tank must also be considered when choosing a filtration system.

For example, if the tank is a tall, hexagonal shape, you don’t want a bulky box-style filter taking up valuable swimming space that could be used by your fish and spoiling the overall look of the aquarium. So, in that case, you may prefer to use a hang-on-back filter.

Priming

Priming is the process through which your filter is prepared for use. In the case of aquarium filters, priming usually involves filling the filtration unit with water to get it up and running. If you don’t prime the system, it will run with air in the tubing, rather than water. That may cause the system’s motor to burn out, the unit won’t filter your aquarium water properly, and the system will be very noisy too.

Although priming your filtration system is typically pretty straightforward, if you don’t want the hassle, it’s worth noting that you can buy self-priming or no-prime filter systems. In that case, it’s usually just a case of pushing the primer button a couple of times to draw water through the unit’s tubing and into the reservoir, removing residual air as it does so.

However, in the case of a system that needs priming, all you need to do is fill the unit’s reservoir, and then run the pump to pull the water through the tubing. The unit is then ready for use.

Maintenance

All filter systems require a certain amount of maintenance to keep them running efficiently and avoid problems with water chemistry. The degree of maintenance required varies, depending on the type of system that you have. A common mistake that beginners make is to clean the filter media too often or too thoroughly, which kills the beneficial bacteria that live on the filter media, potentially causing the tank to re-cycle.

Here’s a basic guide to the maintenance requirements of commonly used types of tank filters:

Hang-On-Back Filter

AquaClear - Fish Tank Filter in white background.

HOB filter systems usually need cleaning every few weeks or once a month, when the filter media may also require replacement.

Sponge Filter

Sponge filters are very easy to look after. All you need to do is remove the sponge once a fortnight and rinse it in tank water to get rid of excess sludge and prevent the sponge from clogging.

Canister Filter

care for a filter for an aquarium

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

Under Gravel Filter

UGFs are relatively maintenance-free, as long as you vacuum your aquarium gravel every couple of weeks.

Internal Filter

Filter units that live inside the tank generally need cleaning once a month or so. Simply remove the filter media and rinse it through in tank water, and remove excess sludge from the impeller. Depending on the brand of system you have, you will also need to replace the filter media periodically.

Top 7 Filters For 20-Gallon Tank Reviews

In this section of our guide, we recommend some of the best filtration systems for 20-gallon aquariums that are currently on the market.

1. AquaClear Power Filter

AquaClear Power Filter
  • HOB Filter
  • 100 GPH
  • AquaClear Foam, Activated Carbon and BioMax
Check The Price

 

Aquaclear filters are among the most popular and best quality aquarium filters on the market. Not only is the quality of filtration excellent, but the filters are extremely well-made and have been known to run without problems for over a decade.

The Aquaclear is extremely quiet, provided that you maintain the unit properly and keep the water level topped up in your tank. I have one of these filters operating in a tank in my workroom, and I can vouch that the unit is whisper quiet. In fact, I reckon that my fish make more noise than this filter!

One small bugbear that some users have reported is that the pump’s flow rate can be variable. However, that’s not generally a problem provided that you clean the impeller every couple of weeks.

Pros Cons
  • Competitively priced when compared to many other similar units
  • Easy to clean and maintain
  • Generally reliable and long-lasting
  • Super-quiet
  • Variable flow rate if impeller not cleaned regularly

2. Aqueon Medium Filter Quietflow Internal, 20-Gallon

Aqueon Medium Filter Quietflow Internal
  • Internal filter
  • 130 GPH
  • Filter cartridge, Sponge, Biological
Check The Price

 

The Aqueon Medium Filter Quietflow operates a four-stage filtration system that includes mechanical, biological, chemical, and stationary wet-dry filtration to keep your aquarium water super-clear and healthy for your fish. The high flow rate that the unit produces ensures a high level of dissolved oxygen in the water that makes for healthy, lively fishes.

The pump is designed to run silently, and a clever feature ensures that the pump restarts automatically following power outages or cleaning. The filtration unit is suitable for use with both freshwater and saltwater tanks.

The main downside to this product is that it takes filter cartridges that must be completely replaced roughly every four to six weeks.

You get a lifetime warranty with the unit.

Pros Cons
  • Quiet operation
  • Freshwater and saltwater compatible
  • Generally reliable and long-lasting
  • Lifetime guarantee
  • Filter cartridges are expensive to replace

3. Aqueon QuietFlow LED Pro Aquarium Power Filter

Aqueon QuietFlow LED Pro Aquarium Power Filter
  • Internal Filter
  • 100 GPH
  • 5-stage multi-media filter system
Check The Price

 

Like all Aqueon filters, this one is very well-made, quiet, and reliable. Also, there’s a handy LED warning light that tells you when the filter cartridge is clogged and needs changing.

The actual filter pump is self-priming, so there’s no hassle when it comes to getting the system up and running. The pump is pretty powerful and helps to provide a decent flow rate for good water oxygenation that benefits your fish.

The clever five-stage filtration system keeps the water clean and clear for a great view of happy, healthy fishes. The first filter removes large particles of waste, while the next phase is made from activated charcoal to get rid of discoloration and chemicals. Stage three is the biological element of the system, stage four adds oxygen, and the optional fifth stage takes out any remaining contaminants, such as phosphates.

Pros Cons
  • Starts up automatically
  • 3-Stage Filtration
  • Internal pump helps dampen noise and eliminate leaks
  • Poor durability

4. Fluval 106 External Filter

Fluval 106 External Canister Filters
  • External Filter
  • 145 GPH
  • 3-stage filtration system
Check The Price

 

Fluval has a good reputation for producing high-quality products at affordable prices, and the Fluval 106 Canister Filter is no exception.

The filter has a higher capacity to similar-sized filters thanks to its shape. The unit’s design allows for two media baskets, one for biological filtration and the other for chemical filtration. The system allows for a certain degree of customization, too, as you can swap out carbon and replace it with something else if you prefer.

The flow rate is adjustable, which is a big plus if you have fish that prefer slower water. The system features an instant primer for simple priming, and special noise reduction technology ensures that the unit is very quiet and unobtrusive when operating.

To reduce the amount of debris that gets into the filter, there’s an intake strainer and a mesh guard. That means your tank will be cleaned more efficiently, and maintenance of the system is easier and less hassle.

Pros Cons
  • Super-quiet operation
  • 3-stage filtration system
  • Easy to maintain
  • Expensive when compared to other filters

5. Penn Plax Cascade Canister Filter 500

Penn Plax Cascade Canister Filter 500
  • Canister Filter
  • 115 GPH
  • 3-stage filtration system
Check The Price

 

The Cascade Canister Filter contains two large, stackable containers for the filter media. Although you can use Cascade’s own media, that can come out quite expensive, and there are cheaper alternatives.

The water return process is also customizable in that you can choose to use the regular return chute or the spray bar, both of which are included with the unit.

The unit does take a fair bit of preparation before it’s ready to use, and you do need to prime the canister by depressing the primer button a few times. Once plugged in and switched on, you may notice some air noises until the air is cleared from the unit. However, once up and running, the system is extremely quiet.

The system is easy to maintain. Simply close the water shut-off valves to the two hoses, and remove them from the top of the canister. Pop the canister lid to get to the media trays inside, replace or rinse the media, and reassemble everything.

Pros Cons
  • Super-quiet operation
  • Customizable filtration media
  • Easy to maintain
  • Filter media is expensive

6. Tetra Whisper Power Filter For Aquariums 3 in 1

Tetra Whisper Power Filter for Aquariums, 3 Filters in 1
  • HOB Filter
  • 210 GPH
  • 3-stage filtration system
Check The Price

 

If you’re looking for a decent filtration system that does the job without breaking the bank, the Whisper 3 in 1 Power Filter could be the right choice for you. The unit is well-made with durable parts that are built to last. The flow is adjustable, and the spillway provides oxygenation by agitating the water surface. Although the filter media isn’t of the best quality, it does offer plenty of surface area where beneficial bacteria can grow.

The motor is very quiet so you won’t be disturbed if you want to keep the unit in your bedroom or workspace. Also, the unit does not contain any moving parts, so there’s a greatly reduced chance that it will let you down. Overall, the Tetra Whisper is easy to maintain, efficient, and very well-made for the price.

Pros Cons
  • Quiet operation
  • Inexpensive
  • Self-priming
  • Filter cartridges included
  • Poor quality biological filter media

7. Marina Power Filter

Marina Power Filter
  • HOB Filter
  • 92 GPH
  • 3-stage filtration system
Check The Price

 

The Marine Power Filter is a super-slim unit that clips onto the back of your aquarium. The pump motor lives inside the tank on the intake, and the media is contained within a clear plastic HOB unit. As the motor is submerged, you don’t need to prime it each time it’s unplugged, and the filter height is adjustable so it can be changed to suit different water levels. The motor is also extremely quiet.

The unit has an adjustable flow rate so that you can control the strength of the water movement to suit the requirements of your livestock. The flow is directed horizontally too so that your fish don’t get buffeted around while they swim, and the flow direction helps to agitate the water surface for better oxygenation too.

The system comes with four filter cartridges, two Bio-Carb and two Bio-Clear, both of which contain Cermitek biological filter media.

Pros Cons
  • Adjustable flow rate
  • Easy maintenance
  • Super-quiet running
  • Flow rate could be more powerful

Conclusion

I hope you found my guide to the best filter for a 20-gallon tank helpful and informative.

Of all the products we looked at, our favorite is the Aqueon QuietFlow LED Pro Aquarium Power Filter.

This high-quality filtration system is reliable and well-made for longevity and has a nice LED warning light feature that tells you when the cartridges need cleaning or replacement. The pump is super-quiet, and the five-stage filter media system ensures that the water stays crystal clear and healthy for your fishes.

Newbies to the hobby who have a smaller budget might prefer to try the Aqueon Medium Filter Quietflow Internal filter that offers four-stage filtration for healthy water, a powerful flow rate for good oxygenation, and silent running too, all for an affordable price.

Alison Page has been an avid fish keeper for over 35 years and has owned many different species of freshwater tropical fish including bettas. Currently Alison has two large freshwater tanks. The first tank has two huge fancy goldfish who are almost ten years old and still looking as good as ever. In the other, she has a happy community of tiger barbs, green tiger barbs, corydoras catfish, platys, and mollies.

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