The 8 Best Internal Aquarium Filters, According To An Aquatic Veterinarian

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Internal aquarium filters we recommend on an orange background

The Spruce Pets / Lecia Landis

If you have a fish tank, of any size, you need a filter. Your filter is responsible for taking some of your fishes’ waste and converting it from toxic to less toxic. If you have a small system, or no room for an external filter, you need to take a look at these internal aquarium filters. Internal filters reside inside your tank, usually taking up a bit of room, and need to be kept mostly below the water line, depending on your model.

 No matter what type of filter you choose, routine filter cleaning should be part of your weekly routine. Once you have done your water change, using a gravel siphon, use the collected bucket of water to disassemble and rinse your filter. Using water tank water will preserve your bacterial colonies and keep your tank on the path to success.

Three of these models, FLUVAL U2, JackSuper and Tetra, were all tested in person by the author. We have added on a few more that we have additional first hand experience with in order to guide you to the best model for your tank setup and species. The FLUAL U2 is still the Best Overall choice for its range of sizes, customizable options and ease of cleaning.

Our Top Picks

Best Overall

Fluval Underwater Filter

Fluval U2 Underwater Filter

Amazon

What We Like
  • Best quality sponge

  • Adjustable flow

  • Easy to disassemble and clean

What We Don't Like
  • Tricky setup

Fluval is a quality brand for many aquarium filters. This underwater model is slightly tricky to align the aerator function optimally, but its adjustable flow and quality sponges made up for the finicky setup, which only took us around five minutes.

The Fluval U2 allows for a variety of setup options, making it ideal for a broad spectrum of tank configurations. The adjustable water flow is a particularly useful feature, allowing you to pick whether the filter sprays out its cleaned water from the top, bottom, or across a tall spray bar, minimizing the water pressure output—a perfect pairing for planted tanks. You can even mount the Fluval U2 horizontally, though this option is only really useful for very shallow tanks.

While the Fluval U2 Underwater Filter wasn't the quietest filter we tested, it was close. Plus, with its built-in aeration contributing to your tank's oxygenation it's possible to supplement with a quieter, less obtrusive bubbler.

It was also one of the easiest to clean, making maintenance a cinch. All it takes is tilting the filter forward in order to remove the U2 from its bracket. Then you simply lift the lid for instant access to the easily swappable filter media.The U2's build quality was also high, with our tester giving it the highest possible rating for durability.

Cleaning the sponge and adjusting the flow is easy, with clear instructions provided by the manufacturer. In our four-week testing window, the only issue encountered was needing to adjust the suction cups. But once fixed, there were no further issues. This was the most expensive model we tested, but our testing confirmed its value. 

Dimensions: 4 x 5 x 9 inches | Sizes: 15-, 30-, 40-, and -65 gallon capacities | Filter Media: Foam, carbon, zeolite 

Best Budget

Hygger Aquarium Internal Filter

Hygger Aquarium Internal Filter

Amazon

What We Like
  • Inexpensive

  • Multiple flow options

  • Customizable waterfall function

  • Small footprint

What We Don't Like
  • Limited filter media

  • A little underpowered

If you are looking for a cheaper option for your internal aquarium filter, then you should consider the hygger Aquarium Internal Filter. It contains three chambers for your filter media, and comes preloaded with a less than ideal sponge and ceramic media. It has been reported to be slightly underpowered for its size, so it is not recommended for larger tanks or those with more than a few fish or invertebrates.

 When installing your filter, be sure to take into account how you would like it to function in your tank. The hygger has multiple options for return water flow, including an adjustable outflow nozzle and spray bar with variable aeration. This filter is known for a stronger return flow, which can be adjusted by dialing down the outflow nozzle or by adding more dense filter media.

Dimensions: 2.5 x 2 x 7.5 inches | Sizes: 2-8 gallons, 10-20 gallons, 15-30 gallons | Filter Media: Activated carbon sponge, ceramic bio balls

Best for Betta Fish

Tetra Internal Power Filter

Tetra Whisper Internal Power Filter

Amazon

What We Like
  • Quiet

  • Gentle outlaw

What We Don't Like
  • Hangs below water line (cannot fill tank entirely)

  • No flow adjustment

The Tetra Whisper Internal Filter makes some compromises, but its particular weaknesses also make it a solid pick for bettas and other small tank (less than 4 gallons), low stock aquarium situations.

The worst part of the Tetra Whisper is its filter media, which replaces the dense sponge found in most other filters tested with mesh pads sprinkled with carbon. Whereas sponge filters can last a few years between changes, the Tetra Whisper's filter medium seemed far less durable. Our best recommendation is to replace them with a sponge filter cut to the correct size.

True to its name, the Tetra Whisper was the quietest model we tested since water burbles out of the top instead of spraying through a nozzle. While this makes for a pleasant, babbling brook quality, it also means the Tetra Whisper needs to be placed fairly precisely relative to the water level (it can also be configured to sit on the bottom of a tank). It won't work right if your aquarium is filled to the brim. This finicky positioning combined with poor installation instructions made the Tetra Whisper particularly aggravating to set up.

However, its quiet operation and low flow make this a non-aggressive filter suitable to use in tanks for betta and small fish and minimal aquarium setups. People with large fish species, high population tanks, or have animals that create lots of waste, like turtles, should look elsewhere. 

Dimensions: 4.25 x 4 x 8 inches | Sizes: 1-4 gallons, 5-10 gallons, up to 10-30 gallons, up to 20-40 gallons | Filter Media: Floss cartridge, sponge

Best for Large Tanks

JackSuper Ultra Quiet Filter

JackSuper Ultra Quiet Fish Tank 4-in-1 Internal Aquarium Filter

Amazon

What We Like
  • Highest outflow

  • Adaptor for aeration and wave

What We Don't Like
  • No instructions for cleaning

  • Adaptor did not stay attached

  • Loud

The Ultra Quiet Fish Tank 4-in-1 Internal Aquarium Filter packs a punch. It has multiple chambers and the highest flow of the filters we tested, making it ideal for large tanks or messy goldfish tanks. The JackSuper filter comes in four sizes, accommodating tanks up to 500 gallons. It also came with a wave cycle pump, which we found to be more of a curiosity than a useful function, though anyone looking for a filter for an outdoor pond might find waves useful.

The high-flow, almost jet-like output from this filter makes it an inappropriate pick for tanks with smaller fish or species that commonly have swim impairments, such as bettas. Look for a lower flow model instead. Also, while it may be quiet relative to its high-flow output, the JackSuper Ultra Quiet 4-in-1 was the loudest filter we tested.

Installing the JackSuper 4-in-1 was easy, and, unlike other filters we tested, it never budged once in position. The only issue we encountered came from its optional outflow attachments, which can be swapped depending on whether you want additional aeration or to generate waves on the water's surface. But unfortunately, the high flow kept pushing out the different nozzles. While this won't affect the overall functioning of the filter, it was a nuisance. Once you figure out which nozzle works best for your setup, it might help to glue it in place. 

Dimensions: 10 x 4 x 3 inches | Sizes: 500, 1,000, 1,500, 1,800 liters/hour | Filter Media: Sponge

Best for Small Tanks

Penn-Plax Cascade Internal 400

Penn-Plax Cascade Internal 400

Amazon

What We Like
  • Easy to install

  • Adaptor for spray bar and aerator

  • Easy to remove carbon

What We Don't Like
  • Strict water level requirement

  • No bottom stabilizer

For smaller tanks, the Penn-Plax Cascade Internal filter is an excellent choice. The filter was very easy to set up and had the added bonus of an option for aeration and a spray bar. The aeration hookup allows you to oxygenate the outgoing flow of water from the aquarium, while the spray bar spreads filtered water over the surface like a fountain.

The Cascade's provided filter media was slightly lower quality than our top pick but had an optional carbon canister that could be added or removed easily. The flow adjustment on the top of the filter was a little fidgety, but overall, this is a good quality filter and worth the investment. The water level issue and lack of bottom support make this an excellent option for a small tank.

The biggest issue with this filter was the size. The Penn-Plax Cascade is available in models suitable for 10-, 20-, and 50-gallon tanks, though we found the mid-range model a little underpowered. Finding a permanent attachment seal also proved tricky, especially without anything stabilizing the filter from the bottom.

Dimensions: 8 x 5 x 2 inches | Sizes: Up to 10 gallons, 10-20 gallons, 20-50 gallons | Filter Media: Sponge, carbon

Best Sponge

Aquaneat Aquarium Bio Sponge

Aquaneat Aquarium Bio Sponge

Amazon

What We Like
  • Very easy to set up

  • Low flow for sensitive species (betta, shrimp, fry)

  • Durable sponge

What We Don't Like
  • Limited filtration capacity

  • Can clog easily

For small systems with a low bioload or species that can’t get tossed around too much, consider a sponge filter like the Aquaneat Aquarium Bio Sponge. This type of filtration relies on airlift technology with an airstone running down the center line. As the bubbles flow upward, water is pulled into the sponge for filtration.

Given its limited filtration capability, this type of filter is recommended for shrimp, bettas and growing fry. This filter can take up considerable room in smaller tanks and is woefully underpowered compared to higher flow models. However, your small fish and shrimp will thank you without getting tossed around the tank. Be prepared to clean this sponge frequently since the lower flow allows it to become clogged more easily.

Dimensions: 4.5 x 8 inches | Materials: Sponge with plastic insert | Sizes: Up to 10 gallons, 10-20 gallons, 20-50 gallons, 30-60 gallons | Filter Media: Sponge

Best for Shrimp & Fry

Aquaneat Sponge Filter

Aquaneat Sponge Filter

Amazon

What We Like
  • Limited water flow

  • Multiple filtration layers

  • Easy to clean

What We Don't Like
  • Low filtration capacity

  • Has to be sunk into substrate

Another good option for a low-flow setup is the Aquaneat Sponge Filter. This triangular filter sits in the bottom of your tank, tucked away into a corner and also relies on airlift technology to provide filtration with limited tank disturbance. This filtration is only suitable for shrimp and baby fry.

This filter has a very dense layer of filter media that leads to it being clogged very often and it can be a pain to dig out from the depths of your tank for a cleaning. The layers allow you to swap out various media for whatever suits your tank inhabitants best.

Dimensions: 4.25 x 3 x 3.25 inches | Size: Up to 20 gallons | Filter Media: Sponge

Best Filter Media

AquaClear Foam Filter Insert

AquaClear Foam Filter Insert

Amazon

What We Like
  • Lasts forever

  • Inexpensive

  • Great filtration capability

What We Don't Like
  • Nothing

It’s rare that we have nothing bad to say about a product, but I have been telling all of my clients for years how amazing these filters are. No matter what filter you may have, buy an AquaClear Foam Filter insert, cut it to size and never worry about your filter media again. I have had the same one in my tank for 10 years and it is still just as amazing as it was 10 years ago. It has not rotted or degraded one bit.

Sponge filters such as these are the cornerstone to a successful filter. In our veterinary practice, this is the one filter I recommend to every one of my clients looking to improve their filtration. And, yes, I know it says on the box to replace it every 3 months, but please DON’T! This filter will last for a decade or more, making your fish and your wallet happy.

Dimensions: 2.5 x 5 x 2 inches | Material: Sponge | Size: Fits AquaClear filter series 30, 50, and 70 gallon filters (or can be cut to fit) | Filter Media: Sponge

Final Verdict

Our favorite internal filters are the U-series models from Fluval. They are a great choice for small and large tanks and have room for lots of filter media options to suit your tank. It comes with a high quality sponge and adjustable flow, making it a great option for many tank set ups.

No matter what filter you decide upon, we cannot recommend enough the AquaClear Foam Filter insert. This author has had hers up and running for 10 years and it shows no signs of slowing down. We strongly recommend picking one up and cutting it to whatever size works for your filter.

What to Look for in Internal Aquarium Filters

Filter Media

There are many different types of filter media you may see on store shelves and you can always swap out what is in your filter for something that better suits your tank setup and inhabitants.

  • Sponges: These mechanical filters not only trap debris, but also provide a home for your nitrogen cycle bacteria to live.
  • Carbon: Carbon filters can absorb some compounds from your water, such as chlorine and some phenols, but are not necessary for most aquarium setups.
  • Bioballs: Whether made of ceramic or plastic, these small balls provide housing for good bacteria running your nitrogen cycle.
  • Floss: Another “sponge” providing a tighter network of fibers for collecting debris and housing good bacteria. Beware that these will get clogged much faster than other media on this list.
  • Zeolite: These filter media can be small stones or in pressed shapes. Like carbon, they will absorb some compounds but can also provide homes for good bacteria.

Tank Size

 Many filters are listed by tank size, but they may not take into consideration how many fish and invertebrates reside within your tank. Your “bioload” is made up of all the biologically active members of your tank, including bacteria, that reside within your tank and filter. This is what your filter capacity really needs to handle, but it can be very difficult to tell how much filtration you need.

We recommend going with the tank size that your desired filter falls within and then keep a very close eye on your water quality parameters. It can take up to 4-6 weeks to see full conversion, so try to be patient. Always run your old filter with your new one during this time and keep it handy just in case the new one can’t keep up.

Noise

No matter what filter you choose, it will make some noise. Filters with louder readings have been noted above, but since these are internal filters, the noise may annoy your fish more than you. Yes, fish have ears and can be very sensitive to vibrations with their specialized lateral line organ, so keep an eye on your fish and if they seem to avoid your filter at all costs, you may need to look into a different model or external filter.

Installation

No matter what type of filter you choose, always read the instructions and follow them carefully. This is the best way to ensure proper function of your filter. Many common complaints about filter function are from user error and ignoring the instructions that come in the box.

FAQ
  • Are internal aquarium filters better than external filters?

    Internal aquarium filters are not better or worse than external filters when looking at your overall tank health. The major issue with internal vs. external is you will get wetter when you do maintenance on your internal filters. As long as you properly maintain your filter, it does not matter whether it is internal or external—it is only a matter of preference.

  • Where should you place an internal filter?

    The placement of an internal filter will depend on the manufacturer. As we noted in our testing of the above filters, some types are very particular about where they must be placed relative to the water line, while others can be placed anywhere below the surface. Read your included setup instructions carefully before installing any filter unit.

  • Should an internal filter make bubbles?

    Although many internal filter units contain aeration adaptors, your filter does not have to make bubbles. Unlike most external filters, internal filters will often not have the cascading effect that brings additional aeration and oxygen to your aquarium. However, most systems will have oxygen incorporated at the surface of the air-water interface. If your aquarium is not packed with many large fish (or species like goldfish, which require 20 gallons per fish), you will not likely need additional aeration.

     

     If you are unable to test your tank's oxygen levels, clinical signs of low dissolved oxygen are fish laying on the bottom and exhibiting increased respiratory effort. You can always add a secondary aerator if you are concerned about the oxygen levels in your tank. It is almost impossible to add too much oxygen since the excess will bubble off at the surface.

Why Trust The Spruce Pets?

With over 10 years of experience as a pet fish veterinarian, Dr. Jessie Sanders has seen it all when it comes to aquarium setups. Even in setting up her own fish specialty store, she has hands on experience with many of these models and has used several herself with her own tanks. Filters are a critical part of any fish tank so we take their recommendations very seriously.

Dr. Sanders also provides guidance and product recommendations for the best saltwater filters, aquarium heaters, fish tanks, light kits, powerheads, and more.