10 Best Filters for 20 Gallon Aquariums

You own an aquarium or you’re planning to buy one? If that’s the case, you will likely need to buy a water filter as well. In fact, this article will cover how you can buy the best filter to use with a 20-gallon aquarium.

But first, you should know exactly what type of filter is best suited for such a fish tank. That’s because there are lots of different versions, with different mechanisms too.

What Type of Filter to Choose for a 20 Gallon Aquarium?

There are 3 types of filters that I recommend for 20 gallon fish tanks: hang on back filter, the internal filter and the canister filter. I will talk about all of these in separate. This way, you’ll know how to choose the best version that suits your personal needs. Of course, once I tell you about each, you’ll have the chance to check out 10 of the best filters on the market.

I will not mention sponge filters on purpose. While sponge filters are very effective in smaller fish tanks, they are not suitable for larger aquariums. I would not use sponge filters in fish tanks that are bigger than 10 gallons.

Hang on Back Filter (HOB)

This is probably the simplest filter out of the 3. For instance, you can install it only by clipping it to the back of your aquarium. This is where the name comes from.

The filtration used by this model is pretty simple: the water is drawn into a lift tube, and it goes into a special chamber where it’s going to be cleaned. There are a series of filter media pieces inside this chamber.

The water is pushed through them, and when it’s clean, a pump will push it back into the tank. Depending on the media used by the filter, it can do biological, mechanical or chemical filtering.

Internal Filter

Like its name suggests, this filter is placed entirely inside the fish tank. In other words, it is fully submersible. Because of this, you can place your aquarium wherever you want, because there is no part sticking out of it.

An internal filter works differently than a hang on back filter. But the main idea is the same: it will clean the water inside the tank, if you use it as prescribed. Though it’s worth mentioning that most internal filters are made for smaller aquariums.

Canister Filter

A canister filter is a little similar to the hang on back version, but it does a better job at cleaning. The water is removed from the aquarium with a series of hoses, then pressurized through the filters.

Once the water is clean, it goes back inside the fish tank. This filter also has to be placed outside the aquarium, so more space is needed, when compared to the previous internal filter.

However, a canister filter can do a much better job. This is due to its cleaning process. As you can see, it’s similar to the first type mentioned above, but a canister filter also pressurizes the water through its filter media. Thus, resulting in even cleaner water.

When choosing a filter for your 20 gallons fish tank, you should always consider picking a filter that rated for a bigger aquarium. It is known in the fish keeping community, that most manufacturers tend to rate their filters wrong, because they test them usually without filter media and ideal conditions.

While fish can produce a lot of waste, smaller filters will clog more easily and will be ineffective in filtering the water. This is why it is best to choose an overzied filter.

If you don’t go for a filter that’s powerful enough to clean the water, the aquarium will be unable to sustain itself and you will have algae problems or even fish deaths. So, keep this in mind!

Now, it’s time to talk about the 10 best water filters for a 20-gallon aquarium. All these aquarium filters can be found on Amazon, so I highly recommend checking them out and see which is best for your needs and budget.

Best Filters for 20 Gallon Fish Tanks

Below you will find a short overview of the various filters I consider best for 20 gallon fish tanks:

Filter Name Manufacture Rated Product Price
1. Aqua Clear – HOB Filter 10-30 gallons
2. GRECH CBG-800 Hang-On Back Filter 20-50 gallons
3. Fluval C Power Filter 20-50 gallons
4. Fluval Underwater Filter 20-40 gallons
5. MarineLand Magnum Polishing Internal Filter up to 97 gallons
6. Aqueon Quietflow Internal Power Filter up to 30 gallons
7. Fluval 106 External Filter up to 25 gallons
8. Penn Plax Cascade Canister Aquarium Filter up to 65 gallons
9. Aqueon QuietFlow Canister Filter up to 55 gallons
10. Polar Aurora 3-Stage External Aquarium Filter up to 75 gallons

And here comes the detailed review of each filter:

1. Aqua Clear – HOB Filter

This is our first pick for a good hang on back filter. You can see from its title that a 20-gallon fish tank is more than capable of handling. I mentioned above that you should really look into filters that seem oversized for your aquarium. That’s because this way you can be sure it will stand up to extensive use.

This product comes with built-in biological, chemical and mechanical filtration systems. So, you don’t have to set these up separately by yourself. To make the most out of this filter, it is recommended to clean its components every 2 weeks. This way, you’ll get a much better performance rate.

As a pro, it’s worth mentioning that the product comes with a refiltration system as well that includes an energy efficient pump to lower maintenance costs. Also, the installation is easy and quick. No technical knowledge is required to make it work.

One negative (not for everyone though) is that you should clean it at every 2 weeks as I said above. This is quite frequent compared to some other filters. Even so, the process is easy, and it doesn’t require much skill.


2. GRECH CBG-800 Hang-On Back Filter with UV Sterilizer

This is another hang on back water filter, perfect for a 20-gallon fish tank. Actually, a 20-gallon capacity is the least it needs to work best. So, it’s sized perfectly for your needs. It has a slick design, making it simple to install.

Just like the previous filter, this one also comes with multiple filter medias, but also a UV Sterilizer. You can turn this on and off as you like. It’s used to eliminate algae, and other parasites that might harm your fish.

One of the biggest pros of this filter is its wide usefulness. That’s because fresh water and salt water can both be filtered using it. And on top of that, you can even control the flow of the water that goes into the filter.

It’s worth mentioning as a con that the filter makes quite a lot of noise. The pump isn’t very silent. So, if this is something you don’t want, keep reading and look for another product.

But besides this drawback, there aren’t any others. So, if you don’t mind a louder filter, go for it.


3. Fluval C Power Filter

The Fluval filter works as a hang on back device as well, just like its previous 2 competitors. It’s a quite popular choice for many aquarium owners. This device is suitable for tanks between 20 and 50 gallons. So, it’s exactly what you’re looking for.

It is pretty quick, because it filters 153 gallons of water every hour. In other words, the water in your aquarium will be filtered more than 7 times during a single hour. It comes with an indicator that tells you when the polyfoam needs to be cleaned.

The water is filtered in 5 stages: the first and second ones are the mechanical filtration stages, then the 3rd is the chemical which is done with the carbon filter installed into the device. Stages 4 and 5 are both biological filtrations done with different medias.

There aren’t any cons that need to be mentioned with this product. It does what it claims efficiently and without any problems. They say it’s silent while working, and fortunately that’s true.


4. Fluval Underwater Filter

This filter is from the same company like the previous one. However, there’s a major difference between the 2: the current filter is an underwater filter, not a hang on back one. Though this is the case, this filter is still easy to use and has all the needed properties you’d expect from a top-notch filter.

For instance, it will easily clean 20 gallons of water, because it works with even 40-gallon fish tanks. Besides of this, you can confidently choose it as your next filtration system, if an underwater filter is what you want.

The best advantage that comes with it is the possibility to render the output flow in 3 different positions. When you’re looking for an underwater device, this is a must have feature. All 3 positions come with specific advantages. For instance, the first position (Top Output) will result in maximum oxygenation of the water.

This filter is specifically good if you want a fully personalized aquarium. That’s because by placing it in certain positions, you can create all kinds of customized patterns. For example, by placing it against the wall of the fish tank, you can even create small waterfalls.

A big pro is the fact that the filter is really quiet when functioning at full capacity. This makes it a good fit for people who want to put the aquarium in a silent place, like their work office.


5. MarineLand Magnum Polishing Internal Filter

When I said you should oversize your filter, I bet you didn’t think this device would be among the top 10 candidates. That’s because it works with up to 97-gallon aquariums. Compared with our small, 20-gallon fish tank, you might think this is overkill. But no, not really.

This is true because you need a quality filter, that will work for years. You probably don’t want to buy a new one every 6 months. Due to the fact that the MarineLand filter can handle 97 gallons of water, you can be sure it will work perfectly with 20 gallons. Basically, this is a canister filter.

It can clean 290 gallons of water each hour. Your entire body of water will be cleaned more than 14 times during 60 minutes. Really, this is the biggest positive about this device. When it comes to cleaning water, it does the job in no-time.

The filter media is fully customizable, thus letting you create a special water environment for your sea life. It’s a dual-chamber container, differently from the hang on back filters.

The one drawback with this, is that is takes up a lot of space in your aquarium.


6. Aqueon Quietflow Internal Power Filter

Here’s another good candidate for internal power filtration. Just like you’d expect, it will be fully submerged in the aquarium, so no additional space is required for housing it. You can submerge it in your aquarium vertically or horizontally, it doesn’t matter.

This version works with 30-gallon fish tanks, so your 20-gallon aquarium should be no problem for it. Like the other previous submersible filter that I mentioned, this one also lets you adjust the flow rate and direction of the filtered water. But in addition, you can also regulate the height of it as well.

It’s worth noticing that the filter comes with a 3-stage filtration system for getting rid of debris, toxins and odors and also removes ammonia and nitrates from the water as a biological filtering stage.

The internal filter cartridges are fully replaceable. This means that the device will have a longer working period compared to other products. There is a downside to this though: you have to replace them by yourself, and buy these parts, because they’re not included in the standard package.


7. Fluval 106 External Filter

As you can see, this is another Fluval product. This time, it’s an external filter, so the installation is simple and quick as always. it works with aquariums that contain up to 25 gallons of water.

If you don’t mind a smaller filter that will do the job, this is for you. Something great about the device is the fact that it comes with sound dampening impeller design, so you won’t be bothered by its noise.

Like another item before, this filter also works with fresh and salt water as well. The multi-stage filtration system will do the job, no matter the type of environment you’ll use it in.

You should notice that a 3-year warranty is added to the package. Considering that most other filters only come with 1 or maybe 2 years of warranty, this product becomes even more attractive.

The filter will handle 145 gallons of water per hour. That means that all the water inside your tank will be filtered more than 7 times during 60 minutes. From a small filtering device, this is a great achievement.

The only downside that has to be mentioned, is that if you plan to buy a bigger aquarium, or expand the one you already have, this filter won’t be able to keep up. After all, it works with up to 25-gallon fish tanks.


8. Penn Plax Cascade Canister Aquarium Filter

If a canister filter is what you feel most comfortable with, this product was crafted for you. The Penn Plax filter is a latest generation canister filter that can handle aquariums of up to 65 gallons. So, your 20-gallon fish tank should pose no problems for this product.

The amount of water filtered by it, is 185 gallons per hour. This is a pretty good performance, meaning that your whole environment will be filtered more than 9 times during the span of one hour.

It’s interesting to mention that the Penn Plax comes with flow control, just like a submerged filter. it also contains 2 large media baskets that can be customized to meet all types of requirements an aquarium owner might have.

When you clean the filter, you don’t have to remove the hoses from the aquarium. this makes the maintenance work even easier, thus letting you use the filter again as soon as possible.

If you think about negative parts, there aren’t any specific in this case. The only problem that comes with all canister filters is that you need some dedicated space under your aquarium to place it.


9. Aqueon QuietFlow Canister Filter

This Aqueon product is also a canister filter, like the one before. It was designed to work with both fresh and salt water, used with aquariums of up to 55 gallons.

It’s a little quicker than the previous Penn Plax filter. This one has 200-gallon per hour filtration rate. This results in the water being filtered 10 times in one hour.

It has a unique advantage, because it includes a special water polishing unit that you can hang on the back of your fish tank. This is used to maintain the aquarium filter in a quick and easy manner. It’s also nice they included this for free.

Also, the filter contains all 3 major filtering medias readily installed: mechanical, chemical and biological filters.

Besides these properties, the canister is very similar to the one I talked about before. But if you need a device that works great, this should be a good choice for you.

This filter is compatible with other Aqueon filters. So if you plan on purchasing a hang-on-back filter from Aqueon, you can make the two filters work together.


10. Polar Aurora 3-Stage External Aquarium Filter

This is our last item in this article. This doesn’t mean it’s worse in any aspect. The Polar Aurora is an external canister filter for aquariums that contain up to 75 gallons of water. As an oversized filtering device, this is perfect.

It is probably one of the quickest out there, with a rate of 264 gallons of water per hour. This means that the filtration is completed 13 times during the span of an hour.

Like most filters, this one also grants you the ability to filter the water mechanically, chemically and biologically too. Also, it includes an adjustable spray bar that lets you regulate the output water flow in the tank.

One of the best things about this canister is that you can add additional filtering media. This can result in a special type of water that you need for the fish in the tank. Of course, you don’t necessarily need to do this, because the base system will do its job perfectly.



Now you know about the 10 best water filters used for 20-gallon aquariums. It doesn’t really matter which one you choose in the end, because all of the items mentioned above will do a great job.

You should think about your specific needs and wishes, and you’ll be able to choose a fitting product for your fish tank easily.

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