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The 7 Best Filters For 20-Gallon Aquariums

Keeping an aquarium in your house, whether it contains fish or only plants, requires maintenance and ongoing upkeep. Obviously, one of the things you will always need is a quality aquarium filter.

Without a suitable filter, the aquarium water would become filthy, odorous, discolored, and contaminated with toxins that can harm both fish and plants.

Consequently, you require a filter without a doubt. Today, we'll be discussing 20-gallon aquariums in particular, so BestForPets (bestforpets.org) help you select the best filters for 20-gallon aquariums. Let's not squander any more time and get started!


Fluval C Power Filter



In our opinion, this is the most effective 20-gallon aquarium filter currently available (you can check the current price at Amazon here). There are several explanations for this.

However, the most important reason is because it employs 5-stage filtration, something that few other filters do. The first two stages of filtration are mechanical, the third step is chemical, and the final two stages are biological.

In other words, it will be difficult to find a filter that removes more contaminants from water than this one. The filter cartridges are rather simple to replace, which is always a bonus, and the filter indicates when the foam pads need to be cleaned.

The Fluval C Power Filter is an excellent choice for any 20-gallon aquarium. It can handle up to 119 gallons per hour without difficulty. In other words, if you have a 20-gallon tank, this filter can clean all of the water in it around six times every hour.

In addition, the flow rate of the filter is fully adjustable, which is convenient if you have fish that do not appreciate strong currents.

The coolest aspect of this combination is that the trickling filter works to filter water more effectively when the flow rate is reduced. In other words, decreasing the flow rate of the Fluval C Power Filter does not result in reduced filtering.

The Fluval C Power Filter is a filter that may be hung on the back, a feature we always enjoy. Simply explained, it does not require shelf space and occupies very little space within the tank.

We are continually on the lookout for filters that are effective and don’t consume excessive space.

The fact that you can easily clip this filter onto the rear of your aquarium is, without a question, really convenient. It may not be the largest filter, but it is effective, simple to maintain, and straightforward to install.


  • Very high flow rate for its size
  • Flow rate can be increased or decreased.
  • Outstanding re-filtration system for low flow.
  • Media is quite durable and simple to replace.
  • Extremely simple to mount and install
  • Extremely effective in its duties
  • Amazing five-stage filtration for pristine water


  • Very loud
  • Not suited for volumes more than 20 or 25 gallons


AquaClear Hagen Power Filter



This filter is more than adequate for a 20-gallon aquarium. In fact, this model is compatible with tanks ranging from 5 to 20 gallons.

This specific aquarium filter can process the whole contents of a 20-gallon tank as frequently as seven times per hour, or 140 gallons of water each hour.

Without a doubt, this is really amazing for such a little filter. This filter’s flow rate is adjustable, which is always a plus. However, the most impressive feature is the re-filtration mechanism.

This implies that when the flow rate is decreased, this filter works harder to purify the water it is receiving.

This filter’s ability to hang on the back is always something we like. Other filters may function adequately, but hang on back filters are always extremely space-efficient.

They occupy no space whatsoever. Having them dangle from the aquarium’s rim frees up space inside the tank for fish and plants rather than a filtration system.

Similarly, to put the AquaClear Power Filter, just set it on the aquarium’s rim and secure the clamps. It does not get much simpler than that. The entire filter is fairly sturdy and will not likely leak, although it may be quickly opened for maintenance purposes.

This filter is one of our favorites since the water remains in touch with it for a considerable amount of time. This results in optimal efficiency and minimum energy use. Low operational expenses are something we can all appreciate.

Regarding filtration, this filter is capable of all three primary types of filtration for super-clean water every day of the year.

AquaClear Foam, Activated Carbon, BioMax, and Cycle Guard are included to provide the highest level of chemical, biological, and mechanical filtration. Overall, although this is a simple filter, it does its function flawlessly.


  • Simple to assemble and install
  • Rapid and simple maintenance
  • Simple to change filtration media
  • Each of the three filtering methods
  • Incredible flow of 140 gallons per hour
  • Flow rate is variable.
  • Excellent filtering system
  • Does not consume a great deal of room within the tank.


  • Can get pretty noisy
  • Motor is not of superior grade.


Marineland Bio-Wheel Power Filter



This Marineland Penguin Power Filter is the subsequent filter that we recommend you consider. First and foremost, this specific type is suitable for tanks up to 20 gallons and over 5 gallons.

With a flow rate of 100 gallons per hour, this power filter can treat the water in a 20-gallon tank up to five times each hour. The outcome is water that is as pure and transparent as it can ever be. This filter has a mid-level tube input that enhances water circulation.

Honestly, the Marineland Penguin Power Filter is not particularly impressive, but it gets the job done. It features mechanical, biological, and chemical filtration in a proprietary three-stage process. The incorporation of filter material into compact cartridges makes maintenance a snap.

The cartridges are included with the filter, thus they are not sold separately. The two-piece vented lid prevents this filter from overheating and makes media replacement as simple as possible.

In addition, the provided filter media is of a pretty good grade for very effective and efficient water filtering.

The Marineland Penguin Power Filter is mounted and installed by essentially clipping onto the rear of the tank. It literally takes only two minutes to assemble and install this filter on your aquarium.

The fact that this filter hangs on the back is very convenient. It occupies minimal space both inside and outside the aquarium and is also very energy efficient.

This item is simple to set up, install, and maintain, all of which are significant advantages in our opinion. The Marineland Penguin Power Filter is unquestionably a great option to consider.


  • Media is integrated
  • Media is easily modifiable.
  • Engages in each of the three primary forms of filtering
  • 100 GPH rate of flow
  • Simple to assemble and install
  • Quick maintenance
  • Contains elements that prevent overheating
  • Saves space


  • Can be quite noisy
  • Motor might be improved
  • Must be manually primed


Marina Power-Filter



This is one of the most distinctive-looking filters on this list. This filter is entirely transparent. This may not be to everyone’s liking, but we appreciate the fact that the interior of this filter is always visible.

This makes it easy to determine when the filter material needs to be replaced, it makes it simple to determine if something is damaged or blocked, and it looks extremely good anyhow.

The Marina Power Filter is a power filter with a hang-on-back design, something we always like. Yes, canister and internal filters are effective, but they require a significant amount of room, either within or outside the aquarium.

The Marina Power Filter is nonetheless intended to be elegant and compact, therefore conserving room. The fact that it does not take up any room in the tank is something that your fish will appreciate.

This item is also relatively simple to manage in terms of upkeep. Having the ability to view the interior is really useful, but accessing the interior is just as easy. Regarding simplicity, the Marina Power Filter is a self-priming filter, a trait we always value.

Additionally, we greatly value the fact that this specific filter is quite quiet. Nobody loves a noisy filter, and happily, you do not have to deal with that issue with this filter.

The Marina Power Filter is suitable for up to 20 gallon tanks and has a decent flow rate. The Marina Power Filter’s flow rate is not as high as some of the other alternatives on this list, but it can still process a 20-gallon tank up to three times per hour.

This is not remarkable, but neither is it terrible. We like that the Marina Power Filter’s flow rate may be adjusted to meet our fish.

When it comes to filter media, there is sufficient space for four separate cartridges, allowing it to engage in all three primary forms of filtering via four phases.


  • Very simple to setup and maintain
  • Transparent, a cool feature
  • Simple to attach to the back
  • Does not occupy space within the aquarium.
  • Provision for four filter cartridges
  • Fairly quiet
  • Energy-efficient
  • Modifiable flowrate
  • Does not require priming in any way


  • Durability is uncertain
  • May start to vibrate after extended use


The Tetra Whisper EX 45



The fact that the Tetra Whisper EX Silent Multi-Stage Power Filter is ready to use straight out of the box is one of its strongest characteristics. There is no assembly required, and no priming is necessary.

Yes, this item is pre-assembled and self-priming as well. This item was designed with simplicity and use in mind, which we can certainly appreciate.

Literally every aspect of this filter is straightforward. Simply lay it over the edge of your aquarium and secure it in place with the accompanying hardware, and you’re good to go.

Even better is the fact that this filter is a hang-on-back model with a high filtering capacity and a small footprint. Hang-on-back filters are usually quite convenient since they require so little space inside and outside the aquarium.

This filter works to enhance the degree of water agitation and oxygenation, which are, without a doubt, extremely significant features. Obviously, this item is made to be extremely quiet, which you and your fish will appreciate.

The Tetra Whisper EX Silent Multi-Stage Power Filter has a flow rate of 160 gallons per hour and a capacity of up to 30 gallons.

In other words, it can treat all of the water in a 30-gallon tank more than five times every hour. This implies that your aquarium’s water should constantly be clear and clean.

This is a 3-stage filtration system, which removes all types of water contaminants by mechanical, biological, and chemical filtration. Additionally, you receive specific time strips that indicate when the filter material should be replaced.


  • The pinnacle of simplicity
  • Simple to install, manage, and set up
  • HOB, saves space
  • Quite efficient
  • Utilizes all three forms of filtering
  • Simple to replace filter media
  • Extremely high flow rate, variable
  • Notifies you when media requires updating
  • Comparatively quiet and power efficient


  • The casing is not of superior quality.
  • Motor may not survive very long.


Aqueon Aquarium Power Filter

This is a fantastic small hang-on back filter that doesn’t take up much room, has a reasonable amount of processing power, can be used for both freshwater and saltwater aquariums, and has other cool features as well.

Space & Size

One of the advantages of this specific filter is that it does not take up any room in the aquarium.

This is a hang-on-back filter, so it does require a few inches of space behind the aquarium, but it won’t take up important space within the aquarium, which is something we much enjoy.

Media Forms & Phases

This three-stage filter for smaller tanks is really decent. It has easy-to-change cartridges, which we consider to be a significant advantage.

In other words, instead of replacing media individually, all media is contained within a cartridge. Yes, this item has three filtration processes, including mechanical, biological, and chemical filtration.

A filter change indicator is also incorporated, allowing you to determine when the filter media should be replaced. It is not the most potent choice available, but it should enough for lightly populated tanks.

Processing Ability

The Aqueon QuietFlow PRO Power Filter is capable of filtering between 60 and 80 gallons of water every hour, which is several times the quantity of water in a 20-gallon aquarium, and should be plenty even for a fully filled aquarium.


  • Utilizes no space in the tank
  • Simple-to-replace filter cartridges
  • Extremely simple to setup and maintain
  • Fine for medium packed tanks


  • Not the most resilient
  • Needs a respectable amount of rear clearance


Penn-Plax Cascade Corner Filter



This is a wonderful submersible aquarium filter that fits perfectly into the aquarium’s corner.

It has tremendous processing power, an abundance of filter media, and a few more features you may find useful.

Space & Size

Now, because this is a submersible filter, it must be placed directly in the tank, so it does take up some room.

However, this is a corner filter, which is somewhat uncommon but also highly beneficial because it occupies less space than a filter that is not put in a corner.

It is only a few inches in depth and width, so it is both compact and space-friendly. Really great about the Penn Plax 455 Cascade Corner Filter is that it can be positioned horizontally if desired.

Media Forms & Phases

This filter device has three filtration stages, and yes, this covers all three types.

This aquarium filter combines mechanical, biological, and chemical filtration. Here, it is necessary to change media individually.

It’s not a little cartridge, but the benefit is that you may select the type and quantity of media to place inside.

This type of adaptability is highly advantageous from our perspective.

Processing Ability

Impressively, the Penn Plax 455 Cascade Corner Filter can handle up to 120 gallons of water per hour, which is more than plenty for a tiny 20-gallon aquarium.

It is almost twice as powerful as necessary and is capable of handling aquariums that are densely populated.


  • Incredible water treatment rate
  • All three forms of media
  • Easy to maintain
  • Does not take up a great deal of room within the tank.
  • Mountable on the horizontal


  • A propensity to clog


In terms of fish tank filtration, there are clearly far more than five alternatives. However, for the best filters for 20-gallon aquariums, BestForPets (bestforpets.org) believe the Fluval C4 is the top pick. If you are in the market for a new filtration system, examine them more closely.

Buyer's Guide

What kind of filter should I get for my 20-gallon aquarium?

Various types of aquarium filtration devices are available. A filter for a 20-gallon aquarium can come in numerous shapes or varieties, so you may be unsure of which one is ideal for your tank.

Let’s take a short look at the three most common varieties of 20-gallon fish tank filters.


The first type available is a submersible aquarium filter. These are often straightforward to install and maintain, however you may need to remove specific components for cleaning or media replacement.

These tend to be quite cheap, and they function adequately despite having the least processing power of all filter kinds.

There are little ones that can easily fit in the majority of aquariums, but bear in mind that they go directly into the water and will take up room anyway.

In general, these are reasonably priced and will suffice for an ordinary tank with a moderate number of fish.


Canister filters are the next type of filter you may use for your 20-gallon aquarium. These items are far more effective than any other type of aquarium filter on the market, but they are also considerably more costly.

These are often not too difficult to install, but their upkeep can be a nuisance. On the one hand, they are exterior filters, so they do not take up space within the aquarium, but larger ones will require a great deal of shelf space.

Canister filters are quite outstanding due to their capacity to contain a large quantity of media and media kinds and their capacity to process an enormous volume of water per hour.

A disassembled canister filter revealing its inner workings


Some would argue that the ideal filter for a 20-gallon aquarium is a HOB or hang-on-back filter. These are often average in terms of, well, pretty much everything.

They typically feature adequate processing power, media storage space, a reasonable level of durability, and a reasonable price.

Many people like them for smaller aquariums since they hang on the side or rear of the aquarium and do not take up room within the aquarium.


A frequent misperception exists around 20 gallon tanks. People frequently make the mistake of believing that all 20-gallon aquarium tanks are identical in size and proportions.

Nevertheless, 20 gallon tanks are often available in two variations: the 20 gallon LONG tank and the 20 gallon HIGH tank. By their name, we may deduce their appearance. Consequently, their suggested filter may also be distinct!

Bulky filters are available at the majority of retailers. Due to their size, they are a bit retro, but the most of them are fairly sturdy. Probably the most popular filter for a 20-gallon aquarium is the slim-sized filter, which consumes minimal space within the aquarium.

The smaller the filter, the more room is available for other tank components, such as decorations or fish swimming areas. HOB is an abbreviation for hang on back, as they are known in the community.


What is the definition of priming? Priming is, in our community, the process of preparing a filter for usage in a fish tank. Additionally, enthusiasts must consider the priming component of the filter they select.

Some of us make the error of admiring the filter at the store and purchasing it without knowing how much priming is required, despite the fact that this is a crucial issue for the owner.

The priming requires time, work, and energy from the owner. Some 20 gallon filters are designed to be primed often, while others are “self-priming” and hence require no effort.


Now comes the difficult part. When purchasing a filter for a 20-gallon aquarium, it is crucial to understand its filtering method. The entire tank will be affected by the filter’s filtering process.

Some filters operate slowly but accurately, whereas others operate quickly but less precisely. Consider the volume of water that a filter can handle at a given time before selecting one that is convenient to use on your own schedule.

The processing capacity of the filter is directly proportional to the tank’s water quality maintenance. If you have a large number of fish in your aquarium, the processing power will determine when the water will become dirty or hazardous for your aquatic companions.

Most enthusiasts seek for filters with an adjustable flow rate so they may tailor the filtration process to their personal preferences.

I maintain the majority of my 20-gallon tanks at my home as community tanks, and one of the factors I consider when selecting their filters is the noise level. Now, most individuals do not often consider noise.

Nonetheless, it is one of the least seen variables. The majority of the time, smaller filters are quieter than their larger counterparts.

However, there are powerful filters that are also quieter than the majority; if you are highly annoyed by the white noise filters’ typical sound, do not be reluctant to inquire about the quieter alternatives.


In regards to aquarium filters, maintenance is essential. In addition to investing time, effort, and energy in keeping their tanks clean, owners must sometimes inspect the filter. Some filters are so little that cleaning them might be difficult.

Find a filter with cartridges and parts that are simple to disassemble and clean, as this is a task that must be performed regularly and requires a great deal of time and effort.

Installation is also included in the maintenance of the filter. There are filters that are simple to install and others that are more difficult.

As this is a one-time activity, it does not significantly impact your upkeep. However, installation should always be considered, as a single error might cause the entire tank to fail.

These are only a few of the most important considerations while searching for the finest filter for a 20-gallon aquarium.

Whether you are a novice hobbyist or a seasoned enthusiast, understanding your tools is already half the fight. Keep this list in mind the next time you visit a local store to purchase a filter, and be on your way!


How many filters are required for a 20-gallon aquarium?

This depends on the GPH of your filter. The overall flow rate should be four times more than the tank’s capacity, as a rule of thumb.

Therefore, a 20-gallon aquarium for goldfish should have a total flow rate of 80 GPH. If you are purchasing the Aqueon filter, which can filter 45 gallons per hour, you will want two of them.

How long can a 20-gallon aquarium remain unfiltered?

The majority of fish in a 20-gallon tank cannot survive without a filter. The broad view is that the maximum benchmark would be seven days. However, this estimate is optimistic; it is more likely that the fish can only survive for three to four days.

Ultimately, a 20-gallon tank with associated filter components will eliminate all contaminants from the water. Therefore, removing it will transform the tank into a cesspool.

The fish within will soon be at the mercy of a filthy environment teeming with pathogenic microorganisms. It’s simply not an environment anyone would want their fish to encounter.

It should also be noted that some fish species may thrive without a filter. The most prevalent illustration would be Betta Fish. However, this characteristic does not indicate that a Betta would benefit from a 20-gallon Betta tank with a filter.

A hang-on filter or a canister filter is superior.

Both hang-on filters and canister filters give users distinct advantages. However, it is simple to infer that canisters are superior in terms of performance quality.

This is the reason why these solutions are much more expensive and more appropriate for bigger aquariums. However, this price makes them difficult to sell to certain fish owners.

In these instances, a hang-on filter would be an excellent choice for aquariums bigger than 20 gallons. It also helps that the design of hang-on filters is more easy. Lastly, it is an excellent alternative for those who are just beginning their aquarium hobby.

What size filter is necessary for a 20-gallon aquarium?

A 20-gallon-rated aquarium filter will be readily available for purchasers. It will provide a GPH flow rate of at least 80, which is consistent with the guideline of four times the tank capacity.

However, I’ve observed certain Reddit fans who like to employ filters with greater GPH than is necessary. For instance, they might utilize a 120 GPH (suited for a 30-gallon tank) fish tank filter cartridge in a 20-gallon tank.

Some may argue that this is an effort to prevent manufacturers from misrepresenting a product’s capabilities.

Overall, a 20-gallon aquarium only requires an 80 GPH filter. Therefore, any option discussed in this article would have no problem filtering a 20-gallon long aquarium or a 20-gallon tall tank.

How to set up and utilize

An in-tank filter is quite simple to install. Simply insert the filter within the tank, hang it using the included suction cups, and immerse the tubes.

However, before to doing so, ensure that you have read the handbook. While the majority of filters serve similar purposes, their configurations vary considerably.

Some filters are meant to be hung on the side of the tank to prevent the motor from becoming wet, while others are intended to be entirely immersed. Ensure that you are familiar with the configuration before placing it in your aquarium.

How to clean and maintain

It is essential to clean the in-tank filter, whether it is self-priming or not. Regular cleaning and maintenance will extend its life beyond the duration of the guarantee.

Here’s a rough guideline for when you should clean and maintain your filter:

  • You should clean mechanical filters at least once every four weeks.
  • Replace the activated carbon in chemical filters every four months.
  • When it comes to biological filters, they should be cleaned weekly or whenever blockage becomes obvious.
  • A clean in-tank filter guarantees the survival of all fish and plants placed in the aquarium.

How frequently must I replace my filter cartridge?

Regular cartridge replacement is essential if you want your aquarium’s fish and plants to thrive.

Failure to do so may result in the death of your fish due to debris, chemicals, and undesirable creatures. Change the cartridge every a month or when you notice a substantial drop in water flow.

What advantages can an internal filter offer?

Installing an internal filter offers more advantages than you may realize. Among them is its silent functioning. Since the entire filter is submerged in water, there will be no noise emanating from it. The water will mask the noise produced by the filter.

You might also profit from the automated elimination of unwanted floating particles. You will not have to manually remove them all.

The internal filter will accomplish the task. The filter will prevent leftover fish food from discoloring the water or leaving behind toxic substances that might damage the fish and plants.

Lastly, the majority of internal filters require little maintenance. Some are self-priming, which means they pump air and water to clean their channels.

Author Image

Dr. Deborah Fletcher

Deborah R. Fletcher, DVM, is a skilled veterinarian with more than 15 years of experience dealing with companion and exotic animals. She has experience caring for a variety of animals, including household cats and dogs, reptiles, birds of prey, and even primates. Dr. Fletcher is a valuable part of the BestForPets team, where she contributes to their aim of providing pets and their owners with the finest possible treatment and services.

Veterinarian (DVM) Dr. Deborah Fletcher


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