The Best Filters for 20 Gallon Aquarium to Help Your Fish Thrive

A 20-gallon tank or aquarium is very large indeed. It can accommodate 15 to 20 small fish, which can easily get dirty if not cleaned every day. Therefore, it needs proper maintenance and an excellent cleaning system to keep the water clear, clean, and the fish are thriving. If you want to keep your aquarium water in pristine condition at all times, the most suitable way to do so is to use the best filter for 20 gallon aquarium.

Selecting a top-tier 20-gallon aquarium filter is about doing the proper research. Identifying the vital buying factors is your first step in this process. So let's discuss a few of them before proceeding with the product reviews:

  • Size: Compatible filters with 20-gallon aquariums come in all different sizes. Buyers will need to determine which one most suits their tank’s appearance. After all, a fish won’t be happy if an overly bulky filter is in its way.
  • Filtration Process: Aquarium owners should seek out a filter capable of providing efficient results quickly and easily. Otherwise, they may become frustrated with their new filter rather quickly.
  • Maintenance Requirements: Any worthwhile 20-gallon aquarium filter will offer easy maintenance and installation processes. Honestly, buying one with a lousy reputation in either category is a waste of time.
  • Type: Several kinds of filters are available for 20-gallon tanks. But the common ones are the undergravel, canister, and power filters. In most cases, power filters are often the more popular choice due to their versatility.

But before you decide to purchase a filter for your 20-gallon aquarium, you need to know each product's strengths and weaknesses. This article will provide you an in-depth review of several leading in-tank filter brands. This way, you will have an informed decision before finally using the brand that you have chosen.

Best Overall


Marineland Power Filtration

✔ Up to 150 GPH
✔ Quiet
✔ Durable


Premium Choice


Aqua Clear – Fish Tank Filter

✔ Energy efficient
✔ Easy and quick to install
✔ 2-year warranty


Editor’s Choice


Tetra Whisper In-Tank Filter

✔ Efficient cleaning
✔ Simple design
✔ Inexpensive


Top 10 Filter for 20 Gallon Aquarium Reviews 2023

1. Marineland Penguin Power Filtration


If you wish to keep your aquarium free from unwanted particles, unwanted organisms, and unwanted chemicals which cause discoloration, the filter that you should be considering in your shopping list is Marineland Penguin Power Filter w/ Multi-Stage Filtration.

I like so many things about this particular filter. First is the flow rate. With 150 GPH, I know that the water circulates in the aquarium properly. Its adjustable mid-level intake is another thing to be proud of. It uses a Rite-Size B cartridge

Another thing that I really liked about this filter is its versatility. This filter is so strong it can be used with 30-gallon tanks as well. If you are operating on a limited budget (just like me), having this filter in your home would really be a huge blessing. You don't need to purchase a new filter because you just have to use it with your 30-gallon tank or anything in between.

Its three-stage filtration system is also commendable. With this, I am always sure that my aquarium is free of unwanted organisms, unwanted particles, and most of all – harmful chemicals that can cause poisoning and discoloration.

What I don't appreciate about this product is the Bio-Wheel. There are times that it acts up. When I tried to see what was going on, the impeller stopped working for a while. After carefully returning every part to its rightful place, the whole unit worked as intended. I really hope that this was an isolated case.

  • Up to 150 GPH
  • Uses Rite-Size B cartridge
  • Adjustable mid-level intake
  • Can be used with 30-gallon tanks
  • Three stage filtration system
  • Ideal for freshwater and saltwater fishes
  • Quiet
  • Durable
  • Easy to install
  • Bio-wheel acts up sometimes
Considering everything that I've said before, I believe that the Marineland Penguin Power Filter w/ Multi-Stage Filtration is truly an amazing product. It is quiet, easy to install, and it is durable. Its three-stage filtration system is very impressive; your aquarium will always have clean and clear water. Finally, you'd very surprised to see that this filter can also be used with 30-gallon tanks. If you are going to try a flexible and powerful filter for your aquarium, this one will provide you with the kind of performance that you are looking for.

2. Aqua Clear – Fish Tank Filter


Nothing beats a filter that delivers not only top performance but also energy efficiency. If you want your tank to be clean and clear at all times, the top-tier in-tank filter that you should be using is the Aqua Clear 110.

What I liked about this particular filter is it delivers a top-notch filtration system. It has a patented filtration system that allows me to control the water's flow rate without compromising the effectiveness of filtration in the process. Once I turn the flow rate down, 50% of the water that is inside the filter chamber is processed multiple times. This is actually beneficial for fishes and plants that require a slow water flow rate.

Another thing to applaud about this 20 gallon fish tank filter system is its ease of use and installation. Just hang this product on one side of the aquarium, let the pipes go inside the tank, turn on the power, and that's it! The 2-year warranty is also assuring, considering that some in-tank filters are only operational for less than a year. The warranty is available for non-replaceable parts that would not work within the time frame the manufacturers allow. Finally, this filter is energy efficient; it runs in only in 110v of power.

If there's one thing I didn't like about this filter, that would be the occasional noise. The noise may not be too loud, but it's certainly annoying, especially if you come to relax beside the aquarium. The vibration that comes out is tolerable during the day but totally annoying during nighttime.

  • Has a patented filtration system
  • Energy efficient
  • Easy and quick to install
  • Comes with activated carbon, BioMax and Cycle Guard, and Aqua clear Foam
  • Comes with a 2-year warranty
  • Occasional noise
Summing up all of the points that were discussed above, I can say without hesitation that the Aqua Clear Fish Tank Filter is a remarkable product. The filter is quick and easy to install, has a patented filtration system, is energy efficient, and comes with a 2-year warranty. Finally, you don't need to worry about the extra layer of protection because this product comes with Aqua Clear Foam, activated carbon, and BioMax and cycle Guard.

3. Tetra Whisper In-Tank Filter


I don't know about you, but I always trust quality products from companies like Tetra. We can never go wrong with Whisper In-Tank Filter!

This inexpensive and affordable filtration system acts as both a filter and pump for a 20-gallon aquarium or terrarium. Its size is 4.2 in. x 4 in. x 8 in. The product line also has filters for a volume range of 3 to 40 gallons.

I was convinced to buy this because of the BioScrubber and Bio-bag filter cartridges. These are the keys to effective and eco-friendly filtration. These can be changed regularly or as needed.

The design is simple and can fit in small aquariums or turtle tanks. For my aquarium, I hung it inside. You can opt to attach it to the glass using the suction cups.

As for the cleaning, it is super easy! Remove the button so you can reach the impeller. And voila! Clean filter! I was even able to clean the scrubber and filter within 30 minutes.

I thank Tetra for the Whisper system! The motor is under the water, so sound waves and vibrations are lessened. Make sure, though, that the water level follows what is ideal for the unit, like what I did.

The customer assistance team was very helpful. They assisted me when I got a bit of trouble with the impellers and my young betta. It was too small, so I was afraid that it might get caught in between. They taught me how to adjust the impeller speed and assured me that this could not harm the fish. Maybe next time, I should check the size of the impeller first.

  • Efficient cleaning
  • Simple design
  • Fits in an aquarium or terrarium
  • Inexpensive
  • Impellers may be too big
It is always top-rated to go with the brands that are already tried and tested. Tetra's Whisper In-Tank Filter with BioScrubber is an efficient filter system packed in a basic yet satisfying package. Convinced yet?

4. Whisper IQ Power Filter

Whisper IQ Power Filter

An in-tank filter for 20-gallon aquariums should be not only strong enough but also quiet. However, not all filters out there in the market cannot do that. If you are looking for the perfect in-tank filter for your aquarium, perhaps the Whisper IQ Power Filter for Aquariums will satisfy your needs.

What I like about this filter is its quiet operation. This is one of the features that a good in-tank filter should have. I can truly enjoy watching the fish swim around in total peace. This is very practical to use in home offices, libraries, or mancaves where comfortable silence is required.

In addition to the two positive features that I mentioned, this filter is extremely durable. It was able to withstand two accidental falls when I was adjusting the flow rate. It didn't break or had its parts fall apart from the inside.

Another applaudable feature that I truly enjoy about this filter is its adjustable GPH. Other in-tank filters don't have this kind of feature. From 130 GPH, I can bring the flow rate down to 10 GPH, which is really cool. Adjusting the flow rate rally makes my fish happy.

What I don't appreciate about this in-tank filter is its occasional wild vibration. Although I said before that this filter operates quietly, there are some wild vibrations that happen from time to time. This causes me a little discomfort, especially if I'm relaxing near the aquarium, reading a book, or browsing the internet using my mobile phone, I get irritated by the vibrations coming from the filter's motor.

  • Quiet
  • Flow control up to 130 GPH
  • No priming needed
  • Durable
  • Easy to use
  • Sometimes it vibrates wildly
Having said all of the important information above, I can honestly say that the Whisper IQ Power Filter for Aquariums is one of the top-rated filters in the market today. It is quiet, durable, easy to use, and most of all, no priming is needed. Once you have installed it, you can basically just leave it alone and let it do its job. The water is always clean, clear, and fish are definitely thriving. I get peace of mind having this product in my aquarium.

5. Fluval C Power Filter


As much as we want to be always there for our lovely fish, there are times when we can’t. So, it is most suitable to find pet essentials like Fluval C Power Filter to give us peace of mind and assurance whenever we leave them in their aquariums.

There are 3Cs in Fluval's Power Filter Line. I have the C2 model at 119 GPH, which is good for an aquarium with a 30-gallon volume. There are also available C3 and C4 filters at 153 and 264 GPH, respectively. My C2 filter has a dimension of 8 in. x 6 in. x 4.5. in. All Cs have the same filtration system. The only difference is the pump motor capacity.

It boasts its 5-stages of filtration consisting of 2 mechanical, 1 chemical, and 2 biological processes. This includes Poly/Foam, activated carbon, biological C-nodes, bio-screen, motor O-ring, and drip tray pads. All these are important for effective and easy cleaning.

I love that I don't even have to worry about maintenance. The parts of this Fluval 20 gallon filter, especially the cleaning aids, only need regular replacement at least once a year. I was able to buy another Poly/Foam with just a call to the manufacturer.

Installing the unit or removing and reinserting parts is no sweat. You won't need help from their service crew. Cleaning is also easy peasy. I always check the indicators to give me a signal when I should start cleaning.

Noise is also reduced even at the maximum set flow rate. My swimming angels are never stressed!

Well, I should have been careful during the first two months. I was too busy and forgot to clean the filter, so a short clogging happened. After rinsing the poly/foam, everything went back to normal. A piece of advice: always, always check the indicator.

Oh! Did I already mention that it is affordable for a 20 gallon tank filter?

  • Five-stage filtration
  • Noise-free
  • Large capacity
  • Easy to maintain
  • Affordable
  • Possible clogging
With the advanced, large capacity filter system that is dirt- and noise-free, Fluval C Power Filter is definitely a steal!

6. Penn Plax Cascade Aquarium Filter


I have not yet seen any filter that gives a 4D-clean aquarium like the Cascade Hang-On Aquarium Filter with Quad Filtration System of Penn Plax. I literally see, feel, and smell clean water!

Six months ago, I purchased Cascade 100 unit sized 6.5 in. x 6 in. x 6 in. The filtration capacity is 100 GPH, good for up to 20-gallon aquariums of fresh or marine water.

It is a hang-on filter designed for modern aquariums. The self-leveling case keeps the filter level. The adjustable knob and intake tube allow easy filter manipulation.

This has a four-stage filtration process involving mechanical, chemical, and biological clean-up. A PolyFiber floss cartridge entraps particulate matter and serves as breeding spot for good bacteria. Activated carbon-infused Bio-sponge and Bio-Falls help eliminate chemical and biological contaminants.

I love that it is very easy to assemble and install. The set of instructions in the box is a no-brainer. The Cascade line is also available at 20, 80, 150, 200, and 300 GPH capacity.

With great filtration and pumping power comes great noise reduction. The motor is fixed, which may be the reason why it does its job quietly. There has been no leak or malfunction whatsoever for the last six months after my purchase. I love seeing my fish so relaxed!

Customer satisfaction is a Penn Plax priority. There's a 100% money-back guarantee on all orders with a 3-year warranty. Good deal, right?

It was leak-proof when I first installed it. But when I tried to rearrange my house and move the aquarium, I had to uninstall and reinstall the filter setup. Sadly, I saw a few drips, but it was resolved when I adjusted the angle and fixed it properly.

  • Effective Quad-Stage cleaning
  • Noise-free
  • Large capacity motor
  • Possible Leak
This is a great buy for pet owners who are as meticulous as I. With this Penn Plax product, I am sure that my bettas are getting clean water every time. I am looking forward to more months, even years, of using my Cascade 100!

7. Marina S20 Power Filter


There are many things to appreciate about this particular filter. First is the design. I was completely surprised to find out that despite its slim design, its filtration power is comparable to similar brands with larger designs. With only 3.8 x 11.5 x 6.5 inches, who would've thought that this filter possesses a powerful motor that will clean your tank every day? In addition, its slim design allows me to see more of my pet fish and the decorations I have placed inside the tank without the filter getting in the way of my view.

Another positive feature of this in-tank filter is the adjustable flow control. I hate replacing my fish every now and then. Lowering the flow rate provides less stress to fish. Also, with this option, I can lower it down to prevent food debris from entering the filter chamber. But with this feature, I can set the top-tier flow rate that my pet fish needs to thrive inside my 20-gallon aquarium.

Speaking of less stress, I like the way this filter operates. It works completely silently compared to similar models in the market these days. I can relax beside my aquarium all day because I don't hear any kind of noise coming from the filter itself. This is because the motor is completely submerged in the water.

What I don't appreciate about this filter is how expensive the replacement cartridges are. If you don't make any money from your hobby, you will find that replacing busted cartridges will hurt your budget.

  • Slim design but powerful
  • Can be used to filter aquariums up to 20 gallons
  • Self-priming
  • Operates silently
  • With adjustable flow control
  • Easy to maintain
  • Durable
  • Replacement cartridges are expensive
To sum up this review, I can confidently express that the Marina S20 Power Filter is an outstanding product. It works in complete silence, self-priming, easy to maintain, and, most of all – durable. Its slim design provides a powerful performance 24/7. The adjustable flow control is very advantageous to those who are trying different fish. Finally, this in-tank filter is absolutely flexible, it can be used with 20-gallon aquariums.

8. Aqueon Quietflow Power Filter


Are you looking for a way to maximize your aquarium's space without sacrificing the filtration capacity of your in-tank filters? Try using the Aqueon Quietflow E Internal Power Filter.

What I appreciate about this filter is its slim design. It can filter the water without consuming too much space. I can see the fish, plants, and decorations inside the aquarium without my view getting interrupted. Even though it is compact, it can deliver top-notch performance that only some brands in the market provide. With it 60 GPH flow rate, I am confident that my Blue Tangs will thrive properly.

I was surprised to see that this filter auto-starts after a power interruption. There was a sudden power outage in my area, and naturally, all of the appliances went down. When the power was restored, the filter auto-started and resumed its filtration. This pleasant feature would really save me time and effort attending to my fish.

I also like this filter's amazing three-stage filtration system. It provides chemical, biological, and mechanical filtration. With this, I can be sure that the water is free of unwanted organisms such as bad bacteria and fungi, unwanted particles, and nasty chemicals that can lead to water's discoloration.

What I don't appreciate about this filter is the level of noise that it produces. Although it is really tolerable, it gets annoying after some time, especially if you hear it at night.

  • Its vertical design saves plenty of space
  • It has a three-stage filtration system
  • Auto-start pump resumes operation if interrupted
  • Easy to install through suction cups
  • Comes with a limited lifetime warranty
  • Runs with occasional noise
All in all, I conclude that the Aqueon Quietflow E Internal Power Filter is the most suitable filter for 20 gallon planted tank. It is actually powerful, considering its thin design. It is compact and delivers a powerhouse filtration performance. It has a three-stage filtration system which ensures the water's top condition. In addition, this filter comes with an auto-start pump that quickly resumes operation after a power interruption. Finally, you'll definitely appreciate the limited lifetime warranty should you encounter performance issues along the way.

9. Tetra Whisper Power Filter


A highly customizable in-tank filter is truly rare. If you are looking for a good filter that can deliver a solid filtration performance without being too faithful with the manufacturer's spare part recommendation, the top-tier product to use is the Tetra Whisper Power Filter.

When I heard about this particular filter's performance from a friend who uses it, I admit that I was truly curious. I immediately purchased Tetra Whisper Power Filter and replaced my existing in-tank filter with this one. After a few hours of testing it, I have seen that it delivers excellent filtration comparable to other brands in the market these days.

Another thing that I truly enjoyed about this particular product is the highly customizable internal layout. I can place any kind of filter inside. This is really advantageous to those who have a limited budget but in immediate need of good filtration. Finally, I have also observed that this filter requires little to no maintenance. I can enjoy other things that I love without sacrificing most of my time attending to this filter.

I know that it is impossible to find a completely silent filter these days. However, this one is truly louder compared to other known brands. There was a point when I was sure that the water was already clean, I temporarily turned the filter off to enjoy the comfort of silence. But as long as this filter is regularly maintained, I don't think that it will get louder than it already is.

  • Can be used with smaller aquariums up to 20-gallon tanks (also used for 10 gallon aquariums)
  • Uses three filters in one unit
  • Highly customizable internal layout
  • Compact
  • Durable
  • Louder noise compared to other brands
To summarize what has been said above, I can say that the Tetra Whisper Power Filter is indeed a remarkable product. It delivers a top-notch filtration process that will keep your aquarium in pristine condition. What's even more interesting is you can choose the kind of filter that you need to use. This way, you can still ensure that the water in your aquarium remains clean and clear no matter the kind of filter you use inside.

10. Penn Plax Cascade Aquarium Filter


Keeping your pet fish properly aerated all the time can be achieved if the filter that you are using has a spray bar. However, not all in-tank filters have this feature. If you want your fish to thrive for a long time, the canister filter for 20 gallon tank that you need to try is the Cascade Canister Aquarium Filter by Penn Plax.

The multi-stage filtration system works as intended; it removes unwanted particles, keeps the water clean and clear by filtering chemicals, and keeps harmful organisms such as bad bacteria and fungi away. Its large stackable media gives way to multi-stage filtration.

I have observed that this filter comes with a spray bar. I like this little feature because it keeps my fish properly oxygenated. Similar brands, though they perform admirably, do not have this kind of feature. Because the surface of the water is regularly aerated, fishes and plants can thrive properly inside the tank.

When I was unboxing the product, I noticed that the tubes and connectors are of high quality. This is very advantageous to me because I won't have to buy replacements. Just the level of quality is very assuring that I won't be spending an extra dollar just to keep this filter going for a long time.

What I noticed about this 20 gallon canister filter is how difficult it is to prime it for the first time. When I tried to reconnect it, some bubbles came out of the filter connection. I had to do it at least four times to make sure that it would run smoothly. Since that time, the filter has run efficiently with little supervision only.

  • It has a multi-stage filtration system
  • It comes with a spray bar
  • The connectors and tubes are of high quality
  • Self-priming
  • Priming it for the first time is very challenging
In a nutshell, I can confidently express that the Penn Plax Cascade Canister Aquarium Filter is a good product. This has a good multi-stage filtration system which keeps the fish and plants inside the tank healthy. Moreover, the spray bar keeps the fish properly oxygenated at all times. The product is self-priming, so there is no need to worry about regular maintenance. Finally, you can be sure that you will be using this product for a long time because of the high-quality connectors and tubes that come with the package.

What To Look For When Buying A Filter For 20 Gallon Aquarium


The 20 gallon aquarium tank is by far the most versatile tank for most hobbyists around the globe. Both seasoned and upcoming enthusiasts look at the 20 gallon aquarium tank for its great size, as this allow it to serve as a starter aquarium, a species tank, and a breeding tank, among others.

With a tank this famous, it comes to no surprise that people are going to be looking for the right tank filter. However, that can be tricky because a lot of people tend not to know the factors to consider in choosing the right filter for the specifics of your tank. And so I have created this simple list of things that everyone should consider when buying a filter for a 20 gallon aquarium tank!


There is a common misconception about 20 gallon tanks. Most of the time, people make the mistake of thinking that all 20 gallon aquarium tanks are of the same dimensions and sizes. However, 20 gallon tanks usually come in two types: the 20 gallon LONG tank and the 20 gallon HIGH tank. By their name, we are clued in on what they look like. Because of this, their recommended filter could also be different!

Bulky filters are available in most stores. They are a bit old school because of their size, however, most of them are quite durable. Probably the most famous filter for the 20 gallon tank is the slim-sized filter, chosen for the space it occupies inside the tank. The smaller the filter, the more space you have for other tank factors like decorations or swimming areas for the fish. Seasoned enthusiasts mostly opt for hob filters for 20 gallon tank (HOB is short for hang on back, as they are called in the community.) because, ultimately, they give the most useful space for the fish and the décor inside.


What is ‘priming'? In our community, priming is basically the prepping of the filter you are to use on your tank. Enthusiasts should also consider the priming portion of the filter they choose. Some of us make the mistake of admiring the filter in the store and immediately purchase it without the knowledge of how much priming would be involved when in reality, it is a critical factor for the owner. The priming takes time, energy, and effort on the part of the owner. Some 20 gallon filters are made to be primed most of the time, while there are those that are ‘self-priming' and therefore does not require much attention.


Now comes the hard part. When buying a filter for a 20 gallon tank, knowing about its filtration process is of utmost importance. The filtration process undertaken by the filter will reflect on the whole tank. Some filters work slowly and thoroughly, and some filters work faster but not as precisely. Choose a filter that you can easily work with at your own time, considering the amount of water that they can process at a given time.

The processing power of the filter is directly related to the maintenance of the water quality of your tank. If you keep a great number of fish in your tank, the processing power dictates when your tank will get dirty or toxic for your little friends. Most enthusiasts look for filters with an adjustable flow rate in order to control the filtering process for their specific taste.

I keep most of my 20 gallon tanks as community tanks in my home, and one of the things I consider when choosing their filters is the noise. Now, most of us do not usually take noise in consideration. However, it is one of the most unobserved factors. Many powerful filters are noisy, and most of the time, the smaller ones are quiet. However, there are powerful filters that are also quieter than most, and if you are easily irritated by the white noise filters usually make, then do not hesitate to ask stores for the quieter options.


Maintenance is a crucial part when it comes to aquarium filters. Owners spend time, effort, and energy in keeping their tanks clean, and this also means checking on the filter once in a while. Some filters are so compact that cleaning it can sometimes be a hassle. Find a filter that has cartridges and parts that are easy to take apart and clean so that you will not use much time and energy in its maintenance, as this is something that is to be done frequently.

Installation is also a part of the filter's maintenance. There are filters that are easy to install, there are those that are more complex. As this is a one-time process, it does not really take up time in your maintenance. However, the installation should always be considered because one misstep and your whole tank might go array.

All in all, these are just some of the basic factors to consider when looking for the best filter for 20 gallon aquarium. Whether you are just a new hobbyist or a long-time enthusiast, knowing your tools is half the battle already. The next time you visit your local store for a filter, keep this list in mind and be on your way!

Other Important Factors To Consider


What Is A Filter For A 20 Gallon Tank?

To learn what the proper filters is for a 20 gallon tank, one must first ask, “What is a 20 gallon aquarium tank?â€. The 20 gallon tank is probably the most used among the tank types out there. This is rightly so because of its advantageous size, which allows for versatility. This versatility is sought after because the 20 gallon tank can be used in a number of ways, basically drawn down to three.

The 20 gallon tank makes for a good species tank. A species tank is a special kind of tank that aquarium collectors create specifically for only a certain type of fish. There are many reasons collectors set up a species tank. First and foremost is fascination. Some enthusiasts, myself included, enjoy just seeing their favored species swim together in a tank of their own. The second is behavioral. Fish behavior is an important factor to consider in our line of hobbies. Some fishes can be territorial and aggressive, fighting off and even eliminating other species. Some can be timid and slow and are then consumed by predatory fishes. Some fishes just really prefer to be with their species. The third reason is health, like when certain species require unusual set-ups that just would not be beneficial for other species. Basically, when the environment needs to be fine-tuned just for a special species, then creating a separate tank becomes a need. For these reasons, collectors make use of the 20 gallon tanks as separate species tanks.

The 20 gallon tank is also known for breeding use. The 20 gallon breeding tank is common nowadays, especially for professional collectors and breeders, because it has just the right dimensions. For as long as the fish you are to use will not grow beyond what is limited to the dimensions, then it is fine. Most starting breeders use the 20 gallon tank for breeding fishes like swordtails, platies, and guppies.

The third major use for the 20 gallon tank is the community tank. Arguably the tank-type's most famous variation, the community tank harmoniously brings together different species of different colors and different sizes. For as long as the environment is positive for all the species, the 20 gallon tank gives a great viewing experience for collectors.

After learning how most people use the 20 gallon tanks (and choosing how you would like to proceed with yours), you should then take a look at the filters.

The filters are the owner's second-in-command when setting up a tank. It does everything from cleaning up the mess that the fishes and the plants leave off to influencing the chemical reactions in the water itself. Because the 20 gallon tank is a popular tank, it comes as no surprise that special tank filters built for the 20 gallon tanks are made by companies nowadays. And so only after choosing how you would use the tank should you choose the filter that is right for the job.

How Does It Work?

Tank filters work in different ways, each working in a specialized way of filtration. There are three main filtration types: chemical, biological, and mechanical filtration.

With biological filtration, the tank actually maximizes the use of the beneficial bacteria living inside the tank. Although seemingly invisible, they are actually big in helping the tanks clean. Different types of bacteria and microorganisms help out in breaking down the chemical byproducts produced by the little fishes and the live plants into harmless toxins. This happens through the process of the nitrogen cycle inside the aquarium tank.

Basically, the leftover food, the dead, together with the waste products created by your fishes and plants (and other invertebrates, if you have any) are broken down into ammonia by the beneficial bacteria and fungi. As ammonia is highly toxic to all that is living inside the tank, through biological filtration, it is converted into nitrites thanks to the bacteria known as Nitrosomonas. After converting ammonia to the less harmful nitrites, other bacteria start filtering again. Now, nitrites are truthfully less harmful than ammonia, but still, in small concentrations, it can be harmful for your tank. This time, the bacteria convert the nitrites into almost harmless nitrates. At low levels, these nitrates will not damage the quality of life in the tank. However, it allows for algae build-up.

For this filtration type to work, the tank has to have a filter with the capability to support the beneficial bacteria, as well as give the bacteria and other microorganisms a spot or place they can colonize in order to start the operation.

When it comes to mechanical filtration is more of a ‘physical' clean-up, unlike biological filtration. In mechanical filtration, water is forced to go through a filter media with the use of an air siphon. As the floating debris of leftover feeds, fish corpses and plant byproducts are collected on the filter media, the tank becomes visibly cleaner. Of course, filter media types differ in size, and therefore the results differ when using different kinds. The smaller, finer media are used when trying to clean up the smaller wastes. However, they also clog up faster. This is where owners utilize the use of bigger media in order to catch the bigger wastes before they are able to clog the smaller media as well.

The third type of filtration, chemical filtration, happens as unwanted compounds and toxic elements are removed from the tank water through the use of chemical filters and aquarium chemicals. As today's science creates paths for advancement, it enabled fish enthusiasts to push collecting to the modern era through the utilization of aquarium chemicals. Chemical filtration helps owners improve the quality of the tank's water and, at the same time, greatly affects the water's chemistry so that the frequency of the tank's water change is reduced. All just by the use of chemical media, resins, and formulas.

What Are The Different Types Of 20 Gallon Filters?

There are certainly a lot of filters that can be used for the 20 gallon tanks. However, the three most common 20 gallon filters are the undergravel filter, the canister filter, and the power filter.

The undergravel filter, as its name suggests, is placed under the aquarium gravel (sometimes called aquarium substrate), where it does its clean-up job. From there, it sucks the floating debris through its filter media, cleaning the tank mechanically. Some undergravel filters are able to support biological filtration by allowing bacteria to colonize the areas around it.

The canister filter is a great filter as it provides excellent mechanical, biological, and chemical filtration. Through a siphon tube, it takes water inside and filters it within, using a separate tube to return the water and control the tank's water movement. Although usually pricier than others, it makes up for quality and durability.

The power filter, also known in the community as the ‘hang-on-back' filter, is probably the most used 20 gallon tank out there. You may have seen this filter before when you see other starting hobbyists or families with fish. As the wastes pass through its filters, it can also influence chemical filtration through the use of chemical pads. It also provides a space for beneficial bacteria from inside its cartridge. The power filter is very versatile when it comes to filtration able to help in biological, mechanical, and chemical aspects.

Why do you need a filter for 20 gallon aquarium? (Benefits)

Keeping fish as pet is no easy task, and most enthusiasts know to consider numerous factors in order to provide a healthy environment for their little friends. The water quality, the environment, the waste management are all things that would affect how you raise your pets. And so, keeping this in mind, you should only choose the right materials and equipment. 20 gallon tank filters are built specifically to aid you in creating an amazing fish environment in the 20 gallon tank.

All in all, these are some of the most basic and important factors to consider when choosing the right 20 gallon tank filter for you. Always keep this in mind, so the next time you go to your local store, you know what to look for and why!

Frequently Asked Questions


How many filters do you need for a 20-gallon fish tank?

This depends on what your filter's GPH is. As a rule of thumb, the total flow rate should be four times higher than your tank's capacity. So, a 20-gallon goldfish tank should have a combined flow rate of 80 GPH. For instance, if you're getting the Aqueon filter, which can filtrate 45 gallons per hour, you'll need two of these.

How long can a 20-gallon tank go without a filter?

Most fish inside a 20-gallon tank won’t last too long without a filter. The general consensus is that 7 days would be the maximum benchmark. However, this estimation is a top-case scenario – it’s much more likely the fish can only last 3-4 days.

After all, a 20-gallon tank with filter components attached will clean all the toxins from the water. So removing it will make the tank become a cesspool. The fish inside will soon find themselves at the mercy of a dirty environment filled with harmful bacteria. It’s just not a setting anyone wants their fish to experience.

It’s also worth noting some fish species don’t require a filter to survive. The most common example would be Betta Fish. But this attribute doesn’t mean a Betta would benefit from living inside a 20-gallon Betta tank with a filter.

Which is better: a hang-on filter or a canister filter?

Both hang-on filters and canister filters offer different benefits to users. However, it’s easy to conclude canisters are better, performance quality-wise. It’s why these options are much more expensive and better suited for larger aquariums. But this costly cost does make them a tough sell for some fish owners.

In these cases, a hang-on filter would be a solid filter for 20-gallon aquarium tanks or larger. It also helps that hang-on filters are more straightforward with their design. Finally, it makes a good starting option for anyone who’s recently become an aquarium hobbyist.

What size filter do you need for a 20-gallon tank?

A suitably sized aquarium filter 20-gallon rated will be easy to locate for buyers. It’ll offer a GPH flow rate of at least 80, which is in line with the 4-times tank capacity guideline.

However, I’ve seen some enthusiasts on Reddit who like to use filters with higher than necessary GPH. For instance, they’d use a fish tank filter cartridge with a 120 GPH (suitable for a 30-gallon tank) inside a 20-gallon tank.

Some may say this is an effort to protect themselves against a manufacturer lying about their product’s capabilities. But overall, a 20-gallon tank only calls for an 80 GPH filter. So any option mentioned in this article would have no trouble filtering a 20-gallon long aquarium or 20-gallon high tank.

What are the most trusted 20 gallon tank filter brands?

There are many brands of filters for 20 gallon tanks in the market these days. However, not all of them can deliver the same level of performance that you expect for you own tank or aquarium.

  • Marina S Series
  • Aqueon QuietFlow
  • Penn Plax
  • AquaClear
  • Fluval
  • MarineLand
  • Tetra

With these in-tank filter brands, you can be sure that your tank (and the creatures that live on it) is taken care of.

How to install and use

Installing an in-tank filter is relatively easy. All you have to do is to position the filter inside the tank, hang it on the side or through the provided suction cups, and let the tubes be submerged.

However, before doing so, make sure that you read the instruction manual. While most filters are common in purpose, they certainly have different setups. There are some filters that should be hung on the side of the tank to prevent the motor from being soaked, while there are some that are designed to be submerged completely. Make sure that you know the setup before installing it in your tank.

How to care and clean

Cleaning the in-tank filter, whether self-priming or not, is very important. Regular cleaning and maintenance will extend its lifetime beyond the warranty period.

Here's a general guide to when you should conduct maintenance and clean on your filter:

  • For mechanical filters, you should clean it at least once every four weeks.
  • For chemical filters, replace the activated carbon every four months.
  • For biological filters, clean it every week or if there is an apparent clogging.

A clean in-tank filter ensures 100% survival of the fish and plants that you place inside the tank.

Where to buy?

You can buy in-tank filters in your favorite pet stores. You can also visit shopping places such as Walmart, Costco, and Home Depot. However, if the specific brand or design is not available in your local pet store, you can always try to shop online. is a great website to launch your search for the perfect filter for your aquariums or tanks.

How often should I change my filter cartridge?

Regular cartridge replacement is very important if you wish to see your fish and plants thrive in your aquarium. Not doing so will run the risk of killing your fish due to excess particles, unwanted chemicals, and unwelcome organisms. Change your cartridge once a month or if you see a significant decrease in the flow rate of your water.

What are the benefits of a 20-gallon internal filter?

Installing a 20-gallon internal filter presents various benefits than you could possibly know. One of which is its quiet operation. Since the whole filter is submerged in water, you won't hear any noise coming from the filter. The water will muffle all the noise coming from the filter.

Another benefit that you could enjoy is the automatic removal of unnecessary elements that are floating in the water. You won't have to remove them all manually. The internal filter will do the job for you. The filter will make sure that no leftover fish food will stain the water or leave harmful chemicals that could poison the fish and the plants.

Finally, most internal filters do not require a lot of maintenance. Some of which are self-priming, meaning they pump air and water in order to clear its passages.

What are the benefits of external filter?

External filters, or canister filters, is a cylindrical-shaped filter that holds different media used for filtering the water in the aquarium. It may hold one or more of the following filters:

  • Mechanical filter
  • Biological filter
  • Chemical filter

Each filter has its own purpose in the canister. The mechanical filter strains the unwanted particles away from the water. The biological filter on the other hand, keeps harmful organisms away, such as bad bacteria and fungi. Finally, the chemical filters absorb harmful chemicals that could lead to poisoning the fish or staining the water.

Having said that, the benefits of the external filter are the following:

  • The filtered water is sprayed back into the surface of the water. This agitates the surface of the water, giving way to oxygenation. Because of this, the fish is supplied with a good amount of oxygen. Spraying the water back into the tank also reduces the chance of evaporation.
  • Because this filter is placed externally, it doesn't block the view of the fish swimming inside the tank. It can be placed on the side so that you and your guests can fully see the beauty of the marine creatures that you put there.


Now that you've seen the reviews for the best filter for 20 gallon aquarium, you can now proceed to purchase the one that will suit your specific needs. Always remember, though, that not all of the filters mentioned here have the same performance. Although they were designed to perform a specific task, their performance in actual situations varies a lot. Finally, before installing and using the filters, make sure that you read and understand the instructions in order to prevent experiencing any adverse situations that could affect the living conditions of the fish inside your aquarium.