Last update: November 12, 2022

What Are Bio Balls and Why Are They so Good for Biological Filtration?

You know those small black plastic balls…

The ones that sit inside aquarium filters?

Well, those are called bio balls.

When used properly, bio balls provide powerful biological filtration to your aquarium.

Today, I am going to teach you all about them!

What are bio balls and what do they do?

Closeup on black plastic bio ball open structure

You know those good bacteria in your tank, the ones that convert ammonia into nitrite and then nitrite into nitrate?

Yeah, those bacteria form an essential part of the nitrogen cycle.

Well, they need a home in your aquarium.

Think of bio balls as small plastic houses for nitrifying bacteria.

Did you know? Bio balls can be used in both freshwater and saltwater aquariums.

Now, there is no missing the unusual, open-structure pattern that is found on bio balls.

But this design isn’t there just to be eye-catching. It actually serves a very important purpose.

It increases the surface area of each bio ball.

You see, bacteria likes to cling to the surface of objects.

And, plastic bio balls have been designed to provide as much surface area as possible for the bacteria to cling to.


Allow me to explain.

Let’s compare a bio ball to a regular ball…

Bio ball vs regular plastic ball side by side

Even though both of these balls are the exact same size and shape, the bio ball on the left has much more surface area, making it capable of housing more bacteria than the ball on the right.

Some bio balls even have small pieces of ceramic or foam hiding inside – even more surface area for bacteria to cling to.

Black plastic bio ball split in half with sponge inside

The foam is perfect for growing large colonies of nitrifying bacteria. It’s what makes a sponge filter so good at biological filtration – the process of ammonia and nitrites being converted to nitrates.

While bio balls come in different designs and sizes, they all perform the same function…

Bio balls sit in your filter. As water passes over these balls, the nitrifying bacteria filters your water, removing ammonia and nitrites – dramatically improving the water quality.

With that said, bio balls are a larger media and will work best in a large sump or external filter.

How do you use bio balls?

There seems to be some confusion over how to best use bio balls.

Let me take a moment to clear that up…

Bio balls can be submerged underwater!

In fact, this is how most of you will use them – in your canister, HOB filter or sump.

The only time you wouldn’t place bio balls underwater is if you are using them in a trickle-filter setup.

Ideally, you should use some form of mechanical filtration, such as a sponge or filter floss, before the bio balls. I cover the importance of this later in this guide.

What is the difference between bio balls and ceramic rings?

Bio balls vs ceramic ring noodles aquarium filter media

A question I am often asked is:

Which is better, ceramic rings or bio balls?

The answer isn’t black and white.

You see, both of these filter media are designed to perform differently.

But to properly explain the difference, I need to briefly cover the two types of bacteria that call these two filter media home.

1. Nitrifying bacteria – These bacteria eat ammonia and nitrites. They require oxygen in the water to live. Nitrifying bacteria live on the surface of objects in your aquarium.

2. Denitrifying bacteria – These bacteria eat nitrates. They will only survive if no oxygen is present. Denitrifying bacteria live inside rock, ceramic and other porous materials where no air is present.

Bio balls only carry nitrifying bacteria.

Ceramic noodles can carry both nitrifying bacteria on the surface and denitrifying bacteria inside.

FishLab Tip: You can use more than one type of media in your filter. If you wanted to use bio balls with a different filter media, then go right ahead!

Now, you may be thinking…

That makes ceramic rings the hands down winner since they can carry both types of bacteria.

And, in a lot of ways, you are right. I personally use Siporax for that very reason.

However, it’s a little more complicated than which filter media can carry more bacteria.

You see, ceramic rings increase their surface area through tiny little pores.

These pores are so small that you can hardly see them without a microscope.

Seachem matrix pores for bacteria under microscope

It is in these pores that the bacteria make their home.

The downside of the small pores is that they can become clogged much easier than bio balls.

This is especially true in tanks that don’t have effective mechanical filtration.

While cleaning ceramic rings can help increase their lifespan, some of these pores will become permanently blocked over time.

And when that happens, the biological filtration becomes less and less effective. There will come a time when you eventually need to replace the ceramic rings in your aquarium.

Bio balls, on the other hand, last almost forever.

For me, I find that the benefits of ceramic-style media far outweigh that of plastic bio balls, but then I have a very strict maintenance routine.

If you are looking for a filter media that only carries nitrifying bacteria and requires little maintenance, then bio balls do have their upsides – particularly if you use a trickle filter.

How many bio balls do you need?

The answer to this question depends entirely on the brand of bio balls you purchase.

A general rule of thumb is 2.2 gallons of bio balls per 100 gallons of water.

Bio balls are available in a range of sizes to fit different types of filters – you will be able to fit more small bio balls in the same-sized filter than you will large ones.

Check the manual that came with your bio balls to find the recommended number of bio balls per gallon of water.

While adding fewer bio balls than the instructions recommend results in inadequate filtration, there is no harm in adding more.

What precautions do you need to take when using bio balls?

Aquarium plastic bio ball held between fingers

Now, you may have been warned that bio balls are no good for your aquarium because they can become a nitrite factory.

Dead leaves, poop, uneaten fish food and other waste can become trapped in the bio balls’ patterned structure.

When this happens, the waste can break down and lead to a spike in nitrate levels.[1]

And, this is true…

If you are using them incorrectly!

Bio balls should be used for biological filtration only.

You see, bio balls are designed to house bacteria, not to trap and remove waste from the water column.

That is the job of mechanical filtration, such as sponge pads, foam blocks or filter floss.

A mechanical filter should be in place before the bio balls in your filter system to catch any waste before it reaches your bio balls.

With the pre-filter in place, bio balls become an ammonia and nitrite-fighting super team – just don’t forget to clean your mechanical filter every now and then!

How do you clean bio balls?

If you skipped the mechanical filtration, then you might want to examine your bio balls.

So, take a close look…

If you notice a thick green or brown gunk coating your bio balls, then you need to clean them.

Cleaning bio balls is best done during a water change.

Take some of the water you removed from your tank and swish the bio balls around in it. Don’t scrub or wipe your bio balls as this can remove the bacteria.

You should notice the water turn cloudy as the bio balls move through it – this is the built-up organic matter falling off.

If your bio balls are particularly dirty, you might need to repeat the process.

Important: Do not use any other water than your tank water to clean your bio balls. Using tap water can kill the bacteria in your aquarium, causing your tank to crash – if this happens, you will need to cycle your aquarium again

And, it should go without saying, but don’t use any soap, disinfectant or other cleaning agent – you will kill all the bacteria on your bio balls.


As you see, when used effectively, bio balls can provide an amazing source of biological filtration.

However, I personally still recommend choosing ceramic noodles or a similar filter media such as Siporax because they can also carry bacteria that removes nitrates from the water – something that isn’t possible with bio balls alone.

Do you use bio balls in your aquarium? Let me know in the comments below!

Ian Sterling

I've been keeping fish for over 30 years and currently have 4 different aquariums – it's an addiction. I'm here to teach you everything there is to know about fishkeeping.

I also use this site as an excuse to spend lots of money on testing and reviewing different aquarium products! You can find my reviews here.

Comments (69)

Hi Enwan,

You would need to speak to someone with knowledge about using bio balls for commercial applications, such as farming fish.

I am brand new to all this information. I have two Betta fish in two 5.5 gallons with hang on the back filters. One i have had for 2 years and the other Betta I got about 3 weeks ago. I’m not a big fan of the filtration the filters come with and wanted to customize. I bought ceramic rings, bio balls, and extra sponges. What do you suggest I do from here? I need some guidance. I find a lot of this info on filtration very confusing and just need to hammer down and research.

Hi Megan,

Bioballs and ceramic rings do the same thing – provide your beneficial bacteria with a place to live. If the water quality in your tank is normal (check with a good aquarium test kit), then your filter media is doing it’s job.

If you want some more information, here is some reading you can do on the different types of filtration and how it works:

Mechanical Filtration (sponge, foam, etc.)
Biological Filtration (bioballs, ceramic rings, sponge, etc.)
Chemical Filtration (activated carbon, zeolite, etc.)

Hi, very helpful. I use balls and noodles, but also several layers of coarse sponge, which I think should be similar in effect to the balls. I have also started using bags of small, porous lava rock, available at Home Depot, Lowe’s, etc. It is cheaper than noodles, but supports anaerobic bacteria according to some internet articles. I stock my tanks and refugia with moss and don’t use any chemical filters. My ammonia and nitrites are zero. My nitrates are acceptable. I have to correct pH occasionally. I also use a polishing filter (a heavy felt) and occasional UV for water clarity.

From this article I learned that ceramic rings can house Nitrifying and Denitrifying bacteria. in my case, as Mark says in his August 13th,2018 comment, I also use bio-balls, with a thick layer of Seachem Matrix and lava rocks to house the good bacteria plus a layer of coarse sponge and filter floss to keep dirt off them, no chemical, in a total of three filters due to my over crowed discus tank (guilty) with plants. And as Mark’s tank, so far, readings are zero. Now I really want to know what Mark and I doing is too much?

Hi Hector,

If you have your own system and it works, then you are not doing too much. You can never have too much biological filter media. The fact that you have an overcrowded tank with zero ammonia and nitrite spikes is a testament to what a good job you are doing.

However, to a beginner starting off, it’s easier and cheaper to get by with a mechanical filter (sponge) and single biomedia (usually ceramic rings) and a correctly stocked tank.

That isn’t to say what you are doing is wrong, it isn’t. It’s just a different approach. That’s what makes this hobby so much fun, there is freedom to experiment!

Denitrifying bacteria will thrive when no oxygen is present. Yet, water is partly comprised of oxygen. I’m confused.

Hi Woody,

Excellent question. These bacteria live deep in the pores of filter media, like ceramic rings, where there is little to no water movement. Without water movement, there is not a fresh supply of oxygenated water reaching these bacteria and, in the absence of oxygen, these bacteria then feed off nitrogen. Nitrfying bacteria, on the other hand live on the outside of this filter media and use the oxygen to convert ammonia to nitrite and nitrite to nitrate.

Hi Jim,

All bioballs I have come across have been lightweight and float around in water movement. Some of the ones that have sponge inside can be opened, you could try adding a weight to the middle of these bioballs – it would be time consuming, but it’s a possible solution.

Not a problem Jim, Although I did think of an alternative solution – throw them in a filter media bag? With all of them contained together, they will sink under their own weight.

Ceramic rings are another biomedia that will sink.

Do you have any information regarding the bio-balls shown in you article, how many gallons of water can be handled by a piece of bio-ball? If you don’t, any approximation according to your experience?

Hi there i would like to ask a question but it’s a bit off the subject i hope it’s ok

My question is how to properly set up a top filter

Using filter floss and activated carbon sponge and bio balls and some ceramic rings

I’m trying to find a video recording somewhere that will explain exactly the way of set up but I can’t find it anywhere so I thought to drop a message here.

Thank you so much

all the best

Hi Chris.

The order of filter media, from inlet to outlet is:

Mechanical (sponge)

Followed by

Finer mechanical (filter floss)

Followed by

Bio media (bio balls or ceramic rings)

This way the mechanical filtration will trap debris floating in the water, meaning you won’t have to clean your filter floss or biomedia as regularly.

thank you for this article, if running a saltwater fish only tank, and copper will be used most of the time, in the sump would you still recommend choosing the ceramic noodles over the bio balls ?

would the copper kill the bacteria on the ceramic noodles that removes the nitrates from the water

please let me know what you think

thank you

Hi Adam,

It shouldn’t make a difference which filter media you use, the results will be the same. Copper can kill off beneficial bacteria regardless of what media you use.

Seachem Matrix vs bio balls or rings for a salt water cannister filter? From your previous responses i would assume ceramic rings?

For saltwater, biomedia is not exactly essential – live rock is used as a home for bacteria instead. And it’s far superior to anything you’ll put inside your filter.

Hi Cristian,

Rule of thumb, fast enough for your tank size to run through the filter four times in an hour. So if you have a 20 gallon tank, you would want the filter to turn over 80 gallons of water in an hour.

Hi Ian

I learned a lot of about bioball and ceramic ring from this blog

I have few questions.

1. I understand, only nitrifying bacteria can make their colony in bioballs and nitrifying bacteria work only presence of Air /oxygen . Does it mean that bioballs with nitrifying bacteria needs direct aeration all the time to get direct touch of air /air bubbles ? OR they can use the oxygen dissolved in water?

2. Ceramic ring can hold both nitrifying and de-nitrifying bacteria. But we know nitrifying bacteria work with oxygen, BUT, de-nitrifying bacteria does work without oxygen. My question is how both of them work at same time at same place at same environment?

3. We know, de-nitrifying bacteria work in oxygen less environment and de-nitrifying bio media have to keep in a hidden place where there is no aeration / oxygenation, But water has dissolved oxygen, so how they works with dissolved oxygen in water ?

Kindly reply my questions . I am eagerly waiting to learn it.


Hi iftekhar,

1. Aerobic bacteria in aquariums used dissolved oxygen to break down ammonia and nitrite.

2. If you were to look at your ceramic media under a microscope, you would see that there are gaps between the aerobic bacteria, allowing nitrate to reach anaerobic bacteria. It is worth mentioning that you would need an impossibly large filter with ceramic rings to effectively filter nitrate out of a tank as quickly as it is produced.

3. Because ceramic rings are porous, the de-nitrifying bacteria can work their way DEEP inside the media. Under ordinary filter flow, dissolved oxygen cannot reach them. It’s like how live rock works in a saltwater aquarium.

This is based on my own understanding of the topic. I hope it helps!

“1. Nitrifying bacteria – These bacteria eat ammonia and nitrites. ”

Surely Nitrifying bacteria – eat ammonia and convert it to nitrites. They don’t eat nitrites.

“2. Denitrifying bacteria – These bacteria eat nitrates. ”

The Denitrifying bacteria – These bacteria eat nitrites and convert them nitrates.

Think that makes more sense

Hi Ayacht5,

Sorry, but what you have said here is completely incorrect from a scientific standpoint.

Hi Andre

There isn’t much more that needs to be elaborated on. The user above is arguing the definition of something that has already been defined by science.

Nitrifying bacteria is a group of organisms that oxidizes (“eats”) both nitrite and ammonia.

Hi Vince,

If by “work” you mean replace your filter. Then no. You are essentially cutting off oxygen and water flow to the biomedia, which means the aerobic bacteria won’t be able to do their job.

To help clarify;
Involves two steps with two bacteria groups.
– Nitrosomonas type bacteria (Aerobic) convert Ammonia/Ammonium to Nitrites,
– Nitrobacter type bacteria (Anaerobic) convert Nitrites to Nitrates
– Most Nitrate generation in our ecosystem is assimilated by plants in their biological processes.
Plus plants can offer much larger surface area for denitrification especially aquatic types.
– There are bacteria that process Nitrates (eg Pseudomonas, Clostridium), but many species are pathogenic to humans and plants.

Note: Unlike some Anaerobic bacteria that still perform their processes in the presence of Oxygen, Nitrite consuming bacteria (Nitrobacter) ONLY function in an Anaerobic environment. Also they must be devoid of organic material as it will supplant the Nitrite consumption.

Hi Jessica,

Thanks for adding this extra information. I’m sure readers will find it incredibly useful!

So I stumbled across your page googling info on Bioballs. You were very informative and now I know that they can be submerged. I have a question about the ceramic noodles. When they’ve become “permanently” clogged would a muricatic acid bath not restore their porosity?

Hi Clay,

I can’t answer your exact question. I have no experience restoring Ceramic rings (noodles). Thinking on it, I don’t know anyone in the hobby who even bothers. If you are using mechanical filtration (Coarse + Fine) prior on the filter line, ceramic rings will last years. An occasional, gentle rinse, in fresh water if things look bad will will get them good again. Going further, any ceramic rings that are made from fired clay will eventually begin to dissolve anyway, although this process can take many years. Add the fact that ceramic rings are very affordable, you fully stock most filters for less than $10 and there is honestly little reason to restore them.

Hi Ian

Whats your thoughts on alfagrog?

I have moved down from marine to Cichlids. I have a 400l tanks with 9kg of alfagrog in the main section. I have 1 section remaining empty. I was thinking about filling it with bio balls. I have sponges and a filter sock before it


Thanks Ben

Hi Ben,

I ran into alfagrog when I was visiting the UK. I was curious about it, but when I returned to the USA I discovered it’s basically impossible to come over here, so I haven’t had the opportunity to play with it.

Even so, my thoughts with your setup would be leaning towards using a ceramic media, like Sera Siporax, in theory it should house more beneficial bacteria. Truth be told, it doesn’t really matter which biomedia you put in here, as long as it can accommodate the bioload of your tank. But I always run with the theory “you can never have too mucb biological filtration”


So I am planning on using acarum sponge on top then a mix of ceramic rings and bio balls for a 55 gallon fresh water fancy goldfis tank. Do you thing this is a good plan?

Any tips?


Hi Paloma,

If this is for a hobby aquarium, I’d just use the ceramic rings. There isn’t really an advantage to mixing biomedia here.

Is it ok to put bio balls in with charcoal as in the same level in a canister filter I have filter floss in the bottom and noodles in the next level

Hi Steph,

It shouldn’t make a difference if they are in the same level, but the bio balls should be placed down first. Although if you already have noodles, then there probably isn’t much need for bio balls since they both perform the same function.

Cheers Ian, great blog, lots of learning as I move from a filter to my first sump tank..! eek

It’s a 6 foot tank, for a 20+ year old turtle (they’re quite messy things).

If I’m using the ceramic noodles in the sump, how many do you think I’d need. It feels like I have enough (there’s quite a lot together in a bag, rather than loose) but there’s room for plenty more.

I’m just not sure how much is enough..!


Hi Trev,

I’m probably not the best person to ask here, I fall into the “you can never have too much biofiltration” crowd. If there is spare space, I fill it. I’ll admit, I am not too experienced with turtles, fish are my area of expertise, but if your water parameters are normal then I’d say you have enough. If not, you can always add more!

Also, good thinking on the bag – it will make swapping them out much easier when the time comes, although it should be years before they start to dissolve.

Not really helpful when you have mixed types of bio balls and you don’t have any booklet for them so I think I have to many bio balls and they are basically my only kind of filtration and my dad says nooo you DONT HAVE TO clean them! Little does he know you have to clean them and he won’t get me new bio balls but he never seems to care about filter pads for it and he says he will get me a twenty long for the sump like bruh we already have one and we had a lizard in it but my brother throws a fit when I say we should use it for my sump. He says we can’t use it cause it had lizard sand and poop in it WE CAN WASH IT OUT! Then he says it’s not good for your fish tank! But he just needs to do more research on this. He never listens to me prob cause I’m younger than that forty-seven year old man. He says I’ve had fish tanks longer than you. I’ve done research on saltwater since I got my freshwater tank which was in 2016 I got my saltwater tank this year January 7th soo he had a tank back in 2004 when google wasn’t around so technically I know more then the old man

Hi Tyler,

I feel you, my dad was also a “this is the way we do it, any other way is wrong, you are just a kid” kinda guy. Back in the day I did similar to what you are doing (although google wasn’t around and I had to use the library) but even armed with facts, he thought he was right.

My only advice here is to do your best. If you can get down to your local aquarium club, they might be able to offer freebies and other things that can help you. Also, there’s very likely someone there who is older who will be able to give your Dad advice? My local aquarium club has a member who has been keeping fish for 70 years! Perhaps your dad would listen to someone like that?

Found you article on bio balls very informative. Just to confirm, I have a wet dry filter and half my bio balls are submerged and half are not. Will my filtration still be effective? I was thinking about placing an air stone under my bio ball chamber to add air circulation. Do you think this would make a difference? When my sump was built, they built the baffles a little too high which submerged half my bio balls.

Hi Andy,

I assume you are talking about a trickle filter? As long as water is constantly flowing over them, they will work fine.

Nice Article Ian, Thanks for sharing.
Recently I had a disaster with my 140 L Community tank shrimps (RCS,Blue Dreams, Crystal Reds) and rasboras, neons and a Betta. I did my usual weekly water change and in morning my entire shrimp colony was wiped out. It is an established Planted tank, surprisingly fishes were completely unharmed. I use tap water with Seachem Prime. What do you think possible cause would be? Copper/High Nitrate? one more thing few days back I had greenhair algae on Moss infested entire tank so I know it was going a out of balance. Sorry for the long writing.

Hi Tushar,

It’s hard to say what happened if you are not testing your water. The appearance of green hair algae certainly indicates something is amiss, but unless you test your water, you won’t know what the true cause is.

Thanks for this. Very helpful. I am currently using 18 gallons of bio balls in a trickle setup in a sump (high oxygen) on a 240 gallon display tank. I am intrigued by the fact that this bio filtration only reduces ammonia and nitrites. While my nitrates are manageable – approx 10ppm – I would like zero. I do about 50% water change per week (sometimes more) on a heavily stocked Mbuna tank. Probs have 100 cichlids in the 240! My goal aesthitic goal is over population managed by over filtration. I have recently added plastic bio material into the sump, submerged in filter bags. I added a lot of this – several gallons. Do you think this type of bio filtration, plastic disks that are submerged, will manage nitrates exclusively?

Hi Steve,

Unfortunately, your setup is incredibly unique and, as you know, overstocked. The anaerobic bacteria that can be found in rocks like live rock or ceramic media (that oxidizes nitrates) is unlikely to do so on the scale you want. Bio Balls don’t really manage nitrates, rather ammonia and nitrites. If your end goal is to skip water changes, I don’t see this as being achievable since you will still need to manage mineral replenishment – the stuff fish use for osmoregulation.

With that said, It sounds like an amazing looking tank.

Hi Ian,
I have a pond with a capacity of about 2,500 litres.
I have been using an external UV pressure filter but it clogs up too often and its hard to clean.
I have seen at the local fish shop that they have built a tank which is about a cubic meter and which has alternating layers of foam and bioballs. The water is pumped into the bottom and flows up through the bioball and over the top. There water is always clean.
I was planning on doing the same. What sort of system is this called and is there anything I can read on them.
Thanks in advance,

Hi Paul,

Does water flow over these layers? If so, it could be a trickle filter, although it sounds like it’s operating in the reverse. If the filter is submerged, then it is likely a variation of a multi-layer filter. In aquariums, this design is often repeated in canister filters or sumps.

Hi Ian,

The water flows up from the bottom through the layers and then over the top into the pond.

I am looking for reading material or advice on how best to set the layers up, and what to use apart from bioballs.

Hi Paul,

That sounds like a custom setup. Unfortunately, I can’t think of any dedicated material on setting up this particular unit, since it’s on a considerably larger scale than what would be used on a tank. I think your best bet here would be to post this question in a pond forum, or maybe even to a koi enthusiast group – those guys really know there stuff and would be in a much better position to help you.

Excellent article, thank you. I have a new 50 gallon freshwater tank that came with a pre filter and then a trickle filter system with blue bio balls that are comprised of little fingers so tons of surface area. After reading I feel like the ideal long term for me would be a layer of siporax submerged at the bottom of the filter area for some de-nitrifying and then the blue plastic bio balls on top (some submerged some not). Sound correct? If so how much siporax would you suggest bin that scenario?

Hi Josh,

I would be hesitant to advise this as the amount needed to actually reduce nitrate build up would be very substantial. Think more than would fit in your typical hobbyists filter substantial. Given that you should be doing a weekly water change to restore trace minerals that are essential for fish osmoregulation, which will also lower nitrates, I think it may be a better option to save your money here.

Hi Rana,

More or less surface area is the most important difference. More surface area for beneficial bacteria is better. This can be counteracted to some degree by adding more of a specific media, but in most cases, you are limited by filter space. Otherwise it’s a preference.

Excellent post very knowledgable.
I do have a couple of questions regarding my sump layout.

I have my sump set up the following way filter sock – ceramic rings – bio balls – floss media – pump.

My bio balls do not move and water is still and same as the ceramic rings.

My question is do I put bio balls first then ceramic rings as water passing over bio balls will keep them moving or simply keep it as it is.

Hi Daniel,

If your bioballs don’t move around then it makes little difference the order you put these two biomedia in.


Is it possible to use bio balls for municipal waste water treatment?
what is the surface area of the bio balls in m2/m3?
why mechanical filtration is required before using the bio media?

Hi abdulrahman,

Unfortunately, I can only comment on bioballs in relation to the aquarium hobby. The surface area will entirely depend on the plastic/whether there is sponge in size. Mechanical filtration is important since it prevents the pores of the bio media (ceramic noodles/bioballs etc.) from becoming clogged.

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