Which Internal Filter Is Best For Your Tank? (Top Picks and Reviews – 2020)

This entry is part 4 of 8 in the series Filter types

For small fish tanks or lightly stocked with low filtration needs, an internal filter can completely satisfy the water cleaning requirements.

Angel fish swimming in a small tank

Internal filters can also help you save money. The savings can be reinvested in other accessories for your fin friends.

However, choosing the most appropriate internal filter for your tank is not a simple task. There are many brands on the market, and each brand has different models. How can you make the best choice?

In this article, we’re going to help you choose the best internal filter for your aquarium. Internal filters are brilliant for a few reasons:

  • Maintenance is easy and straightforward.
  • The flow rates are usually optimized for smaller aquariums.
  • They can be very quiet in operation.

For these reasons, and more, we love internal filters.

What about the other filters? Check out our guide featuring the common filter types on the market.

Now, let us show you which internal filter we love the most.

Top 7 Internal Filters Quick Reference

We’ve prepared a simple table to show you the main features of each filter in this review.

You can glance quickly through this information and get an idea of which filter might be best for your tank. Afterwards, we’ll provide more information about each one so you can learn even more about your choice.

Filter feature

Tank size (gallons)
  • Adjustable Flow Rate?
  • Warranty

Whisper Filter

4 - 40
  • N/A

Aqueon Filter

3 - 40
  • 1 year

Fluval Filter

15 - 65
  • 3 years

MarineLand Filter

  • 3 years

Penn Plax Filter

  • N/A

Marina I25 Filter

  • N/A

Elite Mini Filter

  • N/A

In-Depth Filter Reviews

Now we’ll do a brief, intense dive into each of the filters we think you should consider. Their features, recommended fish, and other information will be laid out for you.

Have a look and make your best choice!

#1 – Whisper In-Tank Filter with BioScrubber for Aquariums

The Tetra Whisper In-Tank Filter is brilliant for small fish tanks. Tetra is best known for their fish foods. However, these filters are very reliable and work for years without much hassle.


The Whisper filter uses Tetra’s filter cartridges. These should be replaced every month or so. However, finding replacements is easy.

The filters use filter floss to capture debris in the water column. An activated carbon segment cleans and polishes the water. Finally, the crucial step of biological filtration is done by the BioScrubber pads located near the front of the filter.

The BioScrubber is unique to Tetra’s filters. A solid plastic back forces water to flow evenly over the entire area. Even flow means maximum exposure to the helpful bacteria growing on the scrubbing bristles. This high level of filtration should keep your tank fresh and clean.

One other nice feature is the water return method. Rather than using a powered jet of water, this filter creates a waterfall for your tank. Falling water becomes oxygenated and this boosts the health of your tank.

The loudness of the filter can be adjusted by changing the filter’s height or the water level.

Tetra’s Whisper filters come in several different sizes to suit your needs. There is a mini filter for 3-gallon tanks, a filter for 10-gallon tanks, 20-gallon tanks, and the largest filter is rated for 40-gallon tanks.

Freshwater fish will really enjoy the benefits of this nice filter system. Some people have found the flow rate to be too high for certain fish. Betta fish, for example, may need special consideration so they are not caught by the filter’s current.


  • Compact design fits easily in most tanks
  • Simple clip requires no space outside the aquarium
  • Easy maintenance achieved by swapping filter pads


  • Smaller filters do not come with suction cups
  • Flow rate may be too high for slower fish

#2 – Aqueon Quietflow E Internal Power Filter

Aqueon has created a reliable, affordable power filter to fit inside your fish tank. Their E Series of internal filters is designed to meet the needs of small aquarium owners.


The first feature of these filters is the high flow rate available for the different filter sizes. Aqueon provides models suitable for use in 3-gallon tanks, 10-gallon tanks, 20-gallon tanks, and 40-gallon tanks.

Each size is equipped to produce a flow rate roughly equal to six times its size rating. This means the Aqueon 10 filters about 60 gallons of water per hour. The Aqueon 40 does better and moves around 290 gallons per hour. These flow rates are some of the highest available for these sizes.

All models are designed to manage chemical, biological, and mechanical filtration. This is ideal for removing solid debris, ammonia, nitrites, chemicals, and odors from the water. The filter media is about average in terms of its quality. However, the filter media is very easy to access and change.

Another great feature, which is easily overlooked, are the suction cups used for mounting the filter. There are four cups on the back of the smallest unit. Each suction cup is pretty big, and they work together to make the mounting very secure. Larger filters in the line use two clips as well as two suction cups to keep the filter secure.

Other filter brands use clips (but no cups) to hang on the rim of the tank, but these clips can vibrate and produce excess noise.

The size of this filter and its flow rate make it ideal for different types of tanks. The cascading waterfall created by the return design also works well in alternative tank setups. People have used this filter for paludariums, semi-submerged habitats, and for keeping reptiles and amphibians.


  • Large amount of water pumped per hour
  • Great space for filter media in three stages
  • Small and quiet for its filtration volume
  • Cartridge maintenance is very easy


  • Smallest filter has very limited filter media
  • Internal filters are difficult to disguise in the tank

#3 – Fluval Underwater Filter

Fluval is one of the top manufacturers of filter and aquarium equipment on the market. Their units can be found in fish tanks all over the world.

Their U series, for underwater filter, is a great example of how they built their reputation as one of the best in the business. The new and improved U series is an evolution of their previous version of internal filters.


There have been significant improvements in the design. Here are a few ways they have taken a step forward:

  • The impeller can be accessed for cleaning and maintenance. While simple to maintain, impeller failure is the most common reason for filter failure.
  • A new media insert area has been created inside the filter as well. This enhances the biological filtration ability of the filter.

Another advance, small in size but huge in effect, is the redesign of the filter media chambers.

Most internal filters face a simple problem: they leak dirty water back into the tank during every media change or maintenance session. As soon as you switch off the filter and try to lift it, brown sludge leaks back into the tank.

Fluval has addressed this by changing the lower portions of its casing to solid plastic. This creates a small area at the bottom of the filter for the dirty water to gather rather than leak back into your tank.

The U Series has another trick up its sleeve: it can be flipped horizontally. This extra positioning allows it to function in many different environments. On its side, it is ideal for low-depth tanks such as reptile pools, amphibian habitats, and turtle tanks.


  • Suitable for larger aquariums
  • Versatile positioning allows for supreme installation flexibility
  • Top-opening lid makes maintenance easier
  • Adjustable flow rate and output points increase the system’s capabilities


  • The price is higher than alternatives for the same size of filter

#4 – MarineLand Magnum Polishing Internal Canister Filter

Many people with large tanks (over 20 gallons) use canister or sump filters for all their filtration. Many internal filters are simply not up to the task of providing adequate filtration for big tanks.

Marineland’s Magnum Polishing Internal Canister Filter is an exception to this rule. This relatively compact unit provides three-stage filtration for tanks up to 90 gallons in size.


The best feature of the MarineLand Filter is its versatility. The unit comes with two different filter cartridges:

  • One is designed for providing mechanical, biological, and chemical filtration. It accomplishes this by using a dual chamber canister covered by a filter floss sleeve. The two chambers can be filled with biological filter media and chemical filtration, such as activated carbon.
  • The second cartridge is the polishing cartridge. This beauty contains MarineLand’s micron cartridge to capture tiny particles in the tank. Diatomaceous earth can also be used in this cartridge to really boost its cleaning abilities.

The Magnum is compact in size when its filtration rate is considered. Comparable canister or sump filters will be much larger. Strong suction cups and a sturdy bracket make installation simple.


  • Suitable for large fish tank
  • Strong flow rate and filter output


  • Not suitable for small tanks due to high flow rate
  • Flow rate is not adjustable

#5 – Penn Plax Cascade 600 Submersible Aquarium Filter

Penn-Plax makes some very good aquarium equipment. Their Cascade series of filters are great examples of affordable, high-quality filters for many different fish tanks. The Cascade 600 is a great option for those wanting to boost their tank’s cleanliness without paying too much money.


One great feature of the Cascade 600 is its versatility. This is a fully submersible unit and can be placed vertically or horizontally in the tank.

  • Horizontal placement makes it ideal for shallow pools such as turtle bays, reptile habitats, or even river ecospheres.
  • Vertical placement is common in fish tanks.

An additional level of flexibility if added by the spray bar. You can position the spray bar to reduce water flow and direct it in the best way for their setup.

The Cascade also features an adjustable flow rate. Adjusting the flow while feeding is a common use of this feature. Those keeping slower fish, such as Bettas, will also appreciate having a quality filter that can produce low flow rates their fish will love.

Inside the filter, the theme of customization continues with the filter media design. A simple sponge filter serves as the first stage of filtration. After this, water passes into a filter media cup. This can be filled with whatever seems most suitable for the tank.


  • Adjustable flow rate
  • Flexible installation options
  • Fully customizable filtration media


  • Colored filter may be very visible in the tank
  • Filter media area is not very large

#6 – Marina I25 Internal Filter

Finding a quality filter for very small tanks can be a challenge. Many small tanks are sold with filters that are simply not very good. They move water, might contain a sponge or two, but are not really adequate for any proper setup.

Enter the Marina i25 Internal Filter. This compact unit is designed for small tanks.


It is engineered to provide the correct kind of filtration for tiny tanks without taking up all the available space.

The filter media design is the first great feature of this unit.

  • Water is sucked into the center of the filter cartridge. The water contacts a zeolite chamber first in order to eliminate ammonia.
  • After this, water moves into an activated carbon filter to clean chemicals and odors.
  • A fine mesh filter traps small particles inside the filter so they do not return to the tank. Water returns to the tank via a waterfall at the top.

There is not an option for adjusting the flow rate. However, the filter can be moved so the water level is close to the waterfall output. This will reduce some of the turbulence created by the water output.


  • Small and compact
  • Quiet in operation
  • Very affordable
  • Quality filtration for small tanks


  • No flow rate adjustment
  • Must be installed vertically

#7 – Elite Underwater Mini Filter

Like the Marina i25, this filter from Hagen is engineered for small aquariums. It is only suitable for tanks up to 3 gallons in size. For these micro tanks, however, it does a great job providing clean water for little fish.


One of the best features of this filter is its size. It is very small indeed. Being so small makes it ideal for use in nano tanks where real estate is precious. Plants, rocks, or other decorations can easily be positioned to hide this unit from view.

Inside the filter, filtration is provided by a single chamber filled with a sponge. This provides both mechanical filtration and biological filtration. For tanks less than 3 gallons, more filtration is probably not required. However, since the chamber is open, extra elements could be added to increase its capabilities.

There is a flow rate adjustment feature. This is really useful for reducing the flow rate even further to suit fish that prefer slow-moving water.

Rounding out its features is an optional air tube. This is used to create a venturi effect and add air to the tank. Adding air via the filter is a bit of a tradeoff. The filter will create more noise. However, an additional air pump and air line will not be required.


  • Tiny in size
  • Customizable filter media slot
  • Adjustable flow rate


  • Venturi air line can be very loud
  • Flow rate can be too high for some nano tanks, even when reduced

Our Choices

Now, having shown you the features of the top seven filters on the list, we want to tell you which ones we would choose. We have two choices: the best filter and the most affordable filter.

The Best of The Best: Fluval Underwater Filter

The Fluval Underwater Filter is our choice for the best internal filter available today. Its quality design, durability, and high filtration level make it suitable for almost every tank.  Brilliant filtration quality and flexible installation help this filter achieve spectacular results.

What we like most about this filter is its versatility. The different outputs allow you to design their perfect aquascape. The Fluval becomes a vital part of the system rather than just a black box to be hidden somehow.

The Most Affordable: Whisper In-Tank Filter with BioScrubber

Many people using internal filters are new to this exciting hobby. Budget concerns limit their choice of equipment. Happily, the Whisper In-Tank Filter is both cheap and effective. For a small price, the Tetra Whisper can clean tiny tanks very well. Replacement filter media inserts are cheap as well and can be found in loads of shops and online.


These are our choices for the best internal filters on the market today. Like you, we are still learning about how to enhance our aquascapes to increase our enjoyment.

Have we missed any filters? Please write to us and let us know.

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