What is Best Internal Aquarium Filter You Can Buy in 2021?

Best internal aquarium filter you can buy

An aquarium filter is crucial in fishkeeping to keep the tank clean, clear, and healthy for the inhabitant and Internal filters are one of its types.

Internal filters remain fully submerged in your aquarium water. It is the perfect solution if you can’t afford a canister or hang-on-back (HOB) filter because of space constraints. They are also quite useful and can deliver effective filtration at a much lower price.

You can use internal filters as a standalone filter for small fish tanks or as a backup filter for a larger tank. But, what are the best internal aquarium filters you can buy?

We have had a closer look at several internal filters and handpicked the top 5 in the market. In summary, here are the best internal filters to buy in 2021.

Most internal filters are quiet, runs very smoothly. They are also easy to install using suction cups or brackets that come with the package and require simple maintenance. 

What Is An Internal Aquarium Filter & How Do They work?

The reason they call it internal is that it goes inside your tank. However, some filters remain outside, called external filters, like canisters or HOB (hang on the back) filters.

The media compartment contains all the necessary filtration elements. The filter pump sucks water from the tank and pushes the water to pass through the media chamber. Usually, internal filters contain filter cartridges to provide three-stage filtration; mechanical, chemical, and biological.

Additionally, some brands include UV lights and special algae pads that are capable of preventing algae growth. The most common outflow pattern from the filter is the waterfall; some also use spray bars to evenly distribute the flow.

Internal filters are capable of creating bubbles because it has the provision to suck air from outside. So, while using an internal filter, there is no need to use an air pump because it can oxygenate the water itself.

How to Use an Internal Aquarium Filter? 

To understand the basic operation and get the idea of using an internal aquarium filter effectively, I highly recommend watching the video until the end.

The 05 Best internal aquarium filter review

Fluval U4 has so many unique features that make it my most favorite internal filter. Fluval is a renowned brand for making aquarium filters and other equipment. This one is also not an exception, a high-quality submersible filter suitable to use up to 65 gallons.

Amazingly, Fluval U4 has 3-way flow output. One is from the top for maximum water circulation and oxygenation. Another one is from the middle, and it’s actually an integrated spray bar that provides an even and gentle flow. The last is from the bottom for deepwater agitation. The most important part is, you can adjust the flow according to your tank needs.

Another exciting feature is that it can be placed horizontally as well. The horizontal placement option also makes it suitable for low water tanks, and you can create a decorative waterfall.

It has a three-stage filtration system. You can remove the cartridges from the top access without dismounting the filter. It’s super simple to install and straightforward to maintain. In addition, this internal filter is super quiet, and you cannot hear almost anything while it’s running.

Apart from being a bit pricey, it has no downside, in my opinion. If you want to buy a quality product, it’s an excellent value for the money. In addition, you can use it as a standalone filter for the recommended aquarium size and a supplementary backup filter for larger aquariums.


  • Three-stage filtration system
  • 3-way adjustable flow
  • Super quiet
  • It can be positioned both vertically and horizontally
  • Suitable for freshwater, marine water, and reptile tank
  • Easy access to replace filter cartridges


  • A bit expensive

COOSPIDER Sun JUP-01 submersible filter has gained so much popularity among aquarists. So many users mentioned they had solved algae issues in their tanks with the built-in UV bulbs of this internal filter.

UV sterilizers are very handy to kill unwanted bacteria, viruses, and algae in a fish tank. However, you should not keep the bulb on all the time; otherwise, it may reduce the lifespan of the bulb. You should generally open the UV sterilizer only for 30 to 60 minutes, depending on the tank conditions.

This is a versatile filter, and you can use it in any aquarium, including freshwater, saltwater, or turtle tank. It’s suitable to use in aquariums ranging from 40 to 80 gallons.

Along with the primary filter, it comes with two filter cartridges and one spare UV bulb. So, basically, you don’t need anything extra to set up, and you can use it directly in your aquarium. But, remember to submerge completely in the water.

Like all other internal filters, this one also creates microbubbles; however, you can adjust the bubble amount by regulating the airflow. Meaning you can easily use it in aquariums where a gentle water flow is needed.

I highly recommend this COOSPIDER Sun JUP-01 if you want your money well spent and a crystal clear aquarium; no cloudiness and no algae. The manufacturer also provides a 1-year warranty for their product.

The downsides, it’s comparatively expensive than other internal filters, and some users find it difficult to understand the instruction manual. Still, the images on the package are self-explanatory.


  • Built-in UV sterilizer
  • Efficient in clearing cloudy and green water
  • Suitable to use in all aquariums
  • Remove and prevent algae
  • 1-years of product warranty
  • The amount of bubble is adjustable using a simple knob.


  • Relatively pricey
  • A very few find it difficult to understand the instructions

Tetra Whisper internal filters are probably the cheapest in the market. It has four different sizes, and the largest one can filter up to 40 gallons. The best part is whatever size you buy; you’ll get that under $15.

It mounts on the aquarium with a clip or suction cup included in the package. Water flows from the top like a waterfall, which increases the air-water contact, and oxygenates the water. The operation of this filter is whisper quiet, as the name suggests.

There is no lid on the top, so the filter cartridge remains exposed. That helps in the maintenance; whenever you have clogged cartridges, use two fingers to lift them and replace or clean the filter element. You don’t need to put your whole arm down because the filter top is above the waterline.

Because it’s cheaper and for that, you have to sacrifice some of the features you would have liked. There is no option to adjust the flow; it runs on a preset flow rate. Also, small fish may get sucked in the motor housing, be careful about that. One easy solution is to use some fine mesh to cover the water intake.

If you want to buy a decent filter that is easy on the wallet and provides three-stage filtration, I suggest Tetra Whisper.


  • A Cheap but effective internal filter
  • Provides basic three-stage Filtration
  • Whisper-quiet operation
  • Very convenient maintenance
  • Oxygenate the water well
  • Waterfall pattern flow output


  • Flow is not adjustable
  • Small fish can get sucked in the water intake

Penn Plax cascade 600 submersible aquarium filter is suitable to use for both fresh and marine water. It is capable of filtering tanks up to 50 gallons. However, it could be overwhelming for the unit to clear up all the mess for a turtle tank.

It provides three-stage filtration and has two media chambers; one is for foam and the other one for activated carbon. Here, the foam filters particulate matter and also houses beneficial bacteria. The carbon cartridge removes toxins and harmful chemicals, tannins, and foul odor. A large-capacity media basket allows you to customize with the best filter media available on the market.

The outflow option is adjustable and directional; moreover, the spray bar option increases oxygenation and helps you to distribute the flow evenly in the tank. If you like to hide the filter or have a shallow water tank, you can also place the filter horizontally.

If you want to increase the oxygen level in your tank, you have the provision for connecting the air tube and air muffler to the flow nozzle. Due to the venturi effect, the air will mix with the water. So you don’t need an extra air pump Because you can get both functions from this single filter unit.

Although it’s powerful, it runs silently and is a good one to buy. Price is also reasonable considering the output you get. It’s effortless to install, but few complained that It’s not convenient to open it up for maintenance.


  • 3-stage filtration
  • Customizable media chamber
  • Possible to place both vertically and horizontally
  • Adjustable flow
  • A spray bar distribute the flow evenly
  • No need for a separate air pump


  • Not the best suits for turtle tank
  • Few found difficulties in maintenance

This is a canister-type internal aquarium filter made by Marineland. Marineland is well known for its quality products in the fishkeeping industry.

Along with three-stage filtration, it incorporates another pleated micron filter cartridge that provides crystal clear water. The exciting part is that you can also charge the cartridge with diatomaceous earth (Diatom) to increase the filtration efficiency further.

The main perk of this filter is you can customize and use your preferred media in a large dual chamber media house. In addition, it can filter as much as 97 gallons of water, which is the largest among all internal filters.

The efficiency you can expect is similar to a canister filter, which only sits inside the water instead of outside in a separate cabinet. It could be used in freshwater, saltwater, and turtle tanks where bioloads are higher, and a filter has to clean a lot of mess.

However, you should clean the filter sleeve or replace carbon monthly or as soon as it gets clogged. Few users mentioned that filter cartridges block too early, and you may need to clean or replace them every few weeks.

There are different opinions on how noisy the filter is. Some experienced noise over 5O DB, and others found it extremely quiet. If something is pulled into the impeller, the noise may be created, so unplug it and check for any clogging or damage. You can seek assistance from their outstanding customer service if you have any problems.


  • Three-stage filtration with additional polishing
  • Customizable media chamber
  • Diatom can be charged with the micron cartridge
  • Excellent customer care service
  • Suitable for all aquariums
  • High cleaning efficiency


  • With greater bioload, filter cartridges may got clogged early
  • Some users found it noisy

Wrapping Up

I hope the best internal aquarium filter list will help you to choose one for your tank. My overall choice is the Fluval Underwater U4 filter because it has some fantastic features, and it’s worth the money.

I have also added a video on how to use an internal filter effectively, which I feel could help you deal with any problems encountered during filter operation.

I want to hear your experience using internal filters and what filter you find best; please leave a comment below.

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