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The Best Biological Filter Media For Canisters, HOBs And Other Filters

The best biological filter media for your aquarium depends on several factors including filter type and size, and even your budget…

By Julie Millis
Last updated on

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best biological filter media

Whatever type of filter you own, using a biological stage is a key part of supporting your tank’s natural nitrogen cycle to remove harmful ammonia and keep your water clean and clear. But to find the best biological filter media you need to consider your filter type and tank setup.

We’ve reviewed and assessed several types of bio media and found that overall Fluval Biomax Filter Media is the best biological filter media based on its value and effectiveness in supporting your beneficial bacteria to colonize and grow.

But there are a number of different options depending on factors like the size and type of your filter and your budget. That’s why we’ve included a number of other alternatives to cover all these scenarios.

So let’s take a look at them below!

  1. Best Overall: Fluval Biomax Filter Media
  2. Best Budget: Marineland Canister Filter Bio-Balls
  3. Best For Mixed Media: CNZ Aquarium Filter Media
  4. Best For Premium Biomedia: Biohome Ultimate Filter Media
  5. Best For HOB Filter: AquaClear 20 BioMax Filter Media
  6. Best For Canister Filter: Seachem Matrix Biological Media

Best Biological Filter Media Reviewed

Whether you own a canister, hang on back (HOB) or other filter type, you’ll find the best biological filter media below. Rather than specific pads, we’ve reviewed several bio media types that can be used in different filters so you can customize your media to your needs.

1. Fluval Biomax Filter Media

Fluval Biomax biological filter media


  • Media Type: Bio ring
  • Approximate Size: Each bio ring 0.75 x 0.7 inches
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Canisters and larger hang on back (HOB) filters
  • Best For: Overall

Fluval Biomax is one of the best biological filter media picks available and is our top choice overall. Unlike some smooth ceramic media, the biomax ring has a rough porous surface giving an incredible amount of surface area for beneficial bacteria to colonize.

And the hollow center of each ring allows water to flow through, providing more oxygen to help your beneficial bacteria thrive. It also means even more contact of your wastewater with the media, allowing your bacteria to remove more ammonia to keep your water clean.

You can use Biomax directly in canister filters or add it to a filter bag to make it even easier to change out. At 0.75 x 0.7 inches, each ring is quite large (about the size of your fingertip), but it will still work well in larger HOB filters like the AquaClear 70.

While Fluval recommends you change the media every 6 months, in reality, it can last much longer if you rinse in tank water every 1 or 2 months, and many owners agree with this. Overall this is an excellent bio media at a reasonable price too!

2. Marineland Canister Filter Bio-Balls


  • Media Type: Plastic bio balls
  • Approximate Size: Each bio ball diameter approx. 0.95 inches
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Canisters and hang on back (HOB) filters
  • Best For: Budget

These bio-balls from Marineland are a great option if you want an effective bio media for your canister or HOB filter at an affordable price. As each ball is about the diameter of a quarter dollar (0.95 inches) they’ll fit in a small HOB as well as a larger canister filter.

Whilst they are non-porous, their inner design maximizes the surface area for beneficial bacteria to grow on. They’re also designed to agitate the water as it flows through them to provide better aeration for bacteria, in turn leading to better ammonia breakdown.

Marineland bio balls are really easy to remove and clean, especially if you use a mesh bag in your HOB filter. And many owners report that as well as being affordable, these bio balls will keep for years if you rinse them with aquarium water when they get clogged up.

3. CNZ Aquarium Filter Media


  • Media Type: Plastic bio balls, ceramic bio rings and carbon pellets
  • Approximate Size: Bio ball diameter approx. 1.0 inch, ceramic rings approx. 0.5 inches
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Canisters and some larger hang on back (HOB) filters
  • Best For: Mixed Media

This option from CNZ is great value and gives you 3 types of media in one set. There are two types of biological filter media included, plastic bio balls and ceramic bio rings, as well as carbon pellets for chemical filtration. And used together they will get your water ultra-clear.

As the bio balls are around 1 inch in diameter, they are quite large, and best suited to external canister filters or very large HOBs. The quality of plastic in the bio balls is good for the price and has a great surface area for beneficial bacteria to colonize.

Many owners also report the ceramic media is of particularly good quality and lasts well with minimal maintenance if you keep it free from waste matter. You also get plenty of media in the set, with a 50 piece bag of bio balls, 1 lb of carbon and 1.1 lb of ceramic rings.

Overall this is a great value set of mixed media that lasts well. And with plenty included in the pack, depending on the size of your filter, it can keep you going for several months.

4. Biohome Ultimate Filter Media


  • Media Type: Sintered glass pellets
  • Approximate Size: Each pellet approx. 1.75 x 0.7 inches
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Canister filters
  • Best For: Premium Bio media

Biohome Ultimate Filter Media is a premium biological filter media and that is reflected in the price. But while most bio media supports aerobic nitrifying bacteria (which break down ammonia to nitrite, then nitrate), this product supports anaerobic denitrifying bacteria too.

Denitrifying bacteria break down nitrate, which you usually need to keep under control via frequent water changes. We found it does indeed keep nitrate levels lower, a view supported by several reviewers, meaning you can reduce the number of water changes you need.

As each pellet is around 1.7 x 0.7 inches, it’s quite large media and is best used in external canisters. And users report that using it along with some ceramic bio rings really helps to keep your water parameters under control and your tank clean and clear.

5. AquaClear 20 BioMax Filter Media

AquaClear BioMax Filter Media


  • Media Type: Ceramic bio rings
  • Approximate Size: Mesh bag 3.5 (l) x 2.4 (w) x 1.97 (h) inches
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Hang on back (HOB) filters
  • Best For: HOB Filter

AquaClear 20 BioMax rings are designed for the AquaClear 20 hang on back filter. The small size of the media bag will fit perfectly in this small HOB filter, or other HOBs of a similar size. But you can also get sizes for up to 30, 50, 70 and 110 gallon aquariums.

Although many owners report it does an excellent job at keeping their water clear, be aware that at 3.5 x 2.4 x 1.97 inches the media bag is quite small so you’ll need the larger sizes for bigger filters.

The mesh media bag makes this biological filter media really easy to remove and replace in your filter with very little mess. And the rough, porous surface is very effective for allowing beneficial bacteria to colonize and keep your water ammonia free.

Overall an effective biological filter media for a smaller HOB, but as it’s a very small pack do check the dimensions needed for your filter and go for the larger size if needed.

6. Seachem Matrix Biological Media


  • Media Type: Inorganic pumice stone
  • Approximate Size: Each granule approx. 0.4 inches in diameter
  • Aquarium Type: Freshwater and saltwater
  • Filter Type: Most filter types, but particularly canisters
  • Best For: Canister Filter

Seachem Matrix is inert and inorganic pumice that is a particularly effective bio media for canister filters, although it can also be used in most other types of filters. As each granule is only around 0.4 inches in diameter it will fit smaller filters too.

This media is naturally mined and selected for its high porosity, allowing it to support nitrifying and denitrifying bacteria too. But realistically, while it’s great for supporting the bacteria that remove ammonia, you do need to use a lot of it to see any significant fall in nitrate levels.

As this is a natural product and is inert it won’t affect the pH of your tank. But be aware that some users report other stones such as granite sometimes present due to them being missed when the stones are sorted by the manufacturer.

Overall though this is a highly effective bio media praised by many owners for its ability to leave your water clean and clear after only a short period of use.

Bacteria And Biological Filtration: The Nitrogen Cycle

Biological filtration is a key stage in your filter as it supports the nitrogen cycle within your aquarium. This is the breakdown of harmful ammonia from fish waste into less harmful nitrates. Let’s take a look at the process along with the bacteria involved.

bacteria under microscope

Step 1: Ammonia Production

Most fish are ammonotelic, meaning they excrete waste in the form of ammonia (NH3) or ionized ammonia (NH4+) [1], both directly from the gills and in their feces [2]. More ammonia is released into the water as feces and uneaten food decompose.

Step 2: Breakdown Of Ammonia To Nitrite

Ammonia is highly toxic to your fish and, if left to build up in the water, can cause death at around 2.0 mg/L [3]. Thankfully, this is where the nitrogen cycle comes in, the first step being the breakdown of ammonia (NH3) to nitrite (NO2).

It’s commonly understood that the ammonia-oxidizing bacteria Nitrosomonas spp. are responsible for this step, but further research suggests ammonia-oxidizing archaea are involved [4]. These are tiny organisms similar to bacteria that also colonize your tank.

Step 3: Breakdown Of Nitrite To Nitrate

Nitrite is also toxic to fish, but the final stage breaks it down into nitrate, which is not harmful to fish except at high levels (hence the need to do regular water changes for your tank). Beneficial bacteria including Nitrobacter spp. and Nitrospira-like bacteria perform this step [5].

Benefits of Biological Filter Media

Whilst the beneficial bacteria needed for the nitrogen cycle will naturally colonize throughout your tank, they can often be disturbed by cleaning, glass scraping, or siphoning your gravel.

But by using a biological stage in your filter with the best biological filter media it will give you a number of benefits:

  • Safe Place To Colonize: The right bio media inside your filter will give a dedicated home for the beneficial bacteria in your tank to thrive. And the water flow will bring a supply of ammonia for them to feed on, as well as release new colonies throughout your tank.
  • More Bacteria Means Cleaner Water: The more beneficial bacteria in your biofilter media, the better their ability to break down ammonia and toxins and the cleaner the water will be for your fish.
  • A Natural Filter: Biological filter media is made of non-toxic materials like ceramic or plastic balls. Unlike chemical filtration, bio media acts as a natural filter relying on the bacteria that colonize it to do the work.
  • Can Help Suppress Algal Growth: While algal blooms in your tank can be caused by phosphate, ammonia can also be a cause as algae can take it up [6]. A biofilter with biological media means more beneficial bacteria to break down this ammonia.

Types Of Biological Filter Media

There are many different types of bio media suitable for a range of different filter types and scenarios. Many smaller filters, for example, use replaceable pads in the form of cartridges and the sponge-like material is where the beneficial bacteria colonize.

In filters where you can customize your own media, such as canister filters or hang on backs (HOB), there are many different types to choose from. Some of the best biological filter media types are:

  • Ceramic Rings: These are highly-porous rings or cylinders which are a great fit for canister filters. Their porous nature gives plenty of surface area for beneficial bacteria to colonize.
  • Bio-Balls: These plastic balls can be found in several sizes and will fit many filter types, especially canisters and HOBs. They provide great surface area and help agitate and aerate the water, making a perfect environment for beneficial bacteria to grow on. 
  • Rocks: Porous rocks like lava or pumice make great biological filter media, as again their surface provides the perfect home for beneficial bacteria. These rocks are found in many sizes and will suit several filter types.
  • Bio-Foam: This sponge material not only provides a fantastic surface for beneficial bacteria to grow, but it also acts as a mechanical filter trapping larger debris. Sponge and bio-foam are often used as part of bio media cartridges for smaller filters.

How To Setup Your Biological Filter Media

Whilst there are some simpler types like sponge filters, the majority of aquarium filters tend to support 3 stage filtration. This means they contain mechanical, biological, and chemical filter media to ensure your water is clean and toxin-free.

If you own a filter that takes cartridges you may notice the mechanical layer is the first media in the filter, positioned closest to the inflow of water. This is because the mechanical media acts as a pre-filter to remove larger debris before the water goes on to the next filtration stage.

When setting up a filter with your own customizable media, you need to follow the same approach. Always place your mechanical media in first, before your biological filter media, to avoid it getting clogged with waste matter.

If this happens not only will it make it hard for beneficial bacteria to colonize, but it can also lead to a build-up of more harmful bacteria. If these bacteria start to out-compete the friendly nitrifying bacteria then the breakdown of ammonia in your tank will be much less effective.

How To Choose The Best Biological Filter Media

There are several things to think about when it comes to choosing the best biological filter media for your aquarium. Let’s take a look at some common factors to consider.

plastic ball filter media

Size, Shape And Surface Area

Different types of bio media come in different sizes and shapes. Bio-balls, for example, can come in various sizes but a general size for canister filters is around the diameter of a quarter dollar coin.

This does vary though, so check the manufacturer’s recommendations for the bio media you choose to make sure it’s the right fit for your filter. The best biological filter media will also have plenty of surface area, like porous ceramic, to allow beneficial bacteria to colonize.

Consider Your Filter Type

It’s important to use the right bio media for your filter as not all types are compatible. Canister filters, for example, tend to have large media baskets and you can use a wide variety of bio media in them. But some internal filters can be more limited in the size and type you can use.

Always check your filter to see that your chosen media is compatible and is the right size. You should also ensure that it is the best biological filter media for freshwater or saltwater aquariums. Many work with both, but some are better for saltwater fish tanks.

Cleaning, Replacement And Ease Of Maintenance

The best biological filter media is designed to last for many months before needing replacement, so check how long it is recommended to be used. It’s best not to replace your media for as long as possible, as you’ll lose your beneficial bacteria and it will have to recolonize.

For that reason, when you do change your bio media, only replace around a third and then leave it for around two weeks before replacing the rest. This will allow your existing bacteria colonies to spread to the new media.

You may need to clean your bio media every few months, only if it gets clogged up. Just give it a light swill using existing aquarium water so as not to disturb your bacteria colonies. The best biological filter media often comes in nets you place in your filter which makes cleaning easier.


Whilst bio media is not the most expensive product in the aquarium hobby, some types of biological filter media cost more than others. For example, while ceramic media tends to last very well compared to bio-foam it’s certainly more expensive.

One thing to bear in mind when choosing the best biological filter media is if you do buy a high-quality type it should last a long time before needing replacement, so may be cheaper in the long run. Remember to check reviews on sites like Amazon to help gauge quality.

Our Verdict

Overall we found Fluval Biomax Filter Media to be the best biological filter media based on its ability to support beneficial bacteria, its effectiveness, and price.

But if you want a great value set the CNZ Aquarium Filter Media pack with its generous amount of bio balls, bio rings and carbon is a fantastic choice that will also last well.

Whichever you choose, all the bio media on this list can suit your canister or HOB filter well and is suitable for freshwater or saltwater biological filtration. So you’re sure to find the best option for you!


Take a look below at the answers to some of the most frequently asked questions when it comes to choosing the best biological filter media.

How Much Biological Filter Media Should I Use?

This depends on the size of your tank, type of filter and the type of bio media. Most manufacturers will recommend a volume or usage rate and it’s usually easy to follow.

How Often Should I Clean My Biological Filter Media?

Most bio media will last several months but it’s worth rinsing in aquarium water if it’s clogged around every 1 or 2 months. But don’t over clean as you’ll risk disturbing your beneficial bacteria.

How Often Do I Need To Change My Biological Filter Media?

Don’t change your biological filter media unless it’s really starting to degrade. Biomedia will last many months, and when you do remove it you’ll be removing your beneficial bacteria too. 

Do I Need To Use Other Media In My Filter?

Yes. You’ll at least need mechanical media such as a sponge to act as a pre-filter and trap debris so it can’t clog your bio media. But for the cleanest tank use chemical filtration too.

Photo of author
Julie Millis
Julie has been involved in aquatics for over 15 years. She is passionate about freshwater and saltwater tanks. Julie loves helping with all your fish-keeping questions!

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