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?
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.
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…
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.
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?
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.
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.
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?
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.
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!
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.