co2 diffuser in aquarium

Best CO2 Diffuser Options (Buyer’s Guide)

If you’re an aquarist who wants a beautiful planted tank with lush, vibrant plants, you’ve probably considered going high tech and adding CO2 to your tank. Getting that perfectly aquascaped tank is likely not possible without carbon dioxide fertilization. Using the best CO2 diffuser is an important upgrade for your tank and can help you achieve your green tank dreams. Our favorite CO2 diffuser is the Fibst CO2 Diffuser.

Carbon is required by plants. However, it isn’t easily supplemented in a liquid or solid form like other fertilizers. Instead, it is usually delivered as a gas. Carbon dioxide gas bubbles can be inefficient mechanisms for getting carbon into your tank, which is why aquarists try to figure out the best CO2 diffuser for their aquariums.

6 Best CO2 Diffuser Options:

What is a CO2 reactor and diffuser?

Quick science refresher. In nature, rainfall and evaporation naturally mix CO2 into water. Underwater plants pull this dissolved CO2 from the water and utilize it for photosynthesis, keeping them healthy and vibrant. Photosynthesis is the process by which plants synthesize food (sugar) from carbon dioxide and water, using the power of the sun. In order words, carbon dioxide is necessary for plants to survive.

However, most aquariums are indoors, which eliminates any chance of natural rainfall and thereby natural CO2 infusions. The problem then becomes getting CO2 gas into your aquarium water. What is the best solution?

CO2 injection systems can produce the gas for your aquarium. However, you need a way to get the gas bubbles to dissolve their carbon dioxide in your aquarium water, in a form that is usable by your plants. Meet your new best friend, the CO2 diffuser.

CO2 diffusers convert the gas into fine, microscopic CO2 bubbles. The tiny bubbles help the CO2 more easily dissolve into the water column, converting it into a form that is directly usable by your plants. Your plants can now get the basic elements they need for photosynthesis.

Smaller bubbles have more surface area relative to their volume. More surface area makes it easier for the carbon dioxide to dissolve into the water. In other words, they’re more efficient at getting the CO2 out of the bubble form and dissolved into your water. 

What is the best CO2 diffuser?

Our all-around recommendation for the best CO2 diffuser is the Fibst CO2 Diffuser. It is made from durable stainless steel with an elegant design. As long as your tank isn’t too large, it is a great, affordable option. This option can generate round bubbles, not partial bubbles which helps make the CO2 absorption more efficient.

How does a CO2 diffuser work?

There are two basic CO2 diffuser designs:

  • Mix CO2 and water together to form microbubbles
  • Use a fine screen or membrane to pass large CO2 bubbles through, creating microbubbles 

As you can tell from both of these designs, the goal is reducing the bubble size so they CO2 is more likely to dissolve into your tank, thereby making it more usable by your plants.

The bubble size from the CO2 generator is too large; you will end up wasting a lot of carbon dioxide if you directly injected the CO2 from the generator without a diffuser.

Types of CO2 Diffusers

Here is an overview of the most common CO2 diffuser options:

CO2 reactors

CO2 reactors mix water and the CO2 from your injection system until nearly all the CO2 is dissolved. This is the most efficient, and not surprisingly, expensive option. The limitations of CO2 reactors are: 

  • Not suitable for low-pressure or DIY CO2 generators
  • More difficult to install

Ceramic CO2 Diffuser

Ceramic diffusers typically resemble a disk or thin ceramic membrane. On the exterior rim, they are often glass or stainless steel. In the middle of the disk, they have a layer of ceramic through which the CO2 passes and creates tiny bubbles.

Ceramic CO2 diffusers have a broad variety of designs, meaning you’re likely to find something that works for your tank. Some options sit inside your aquarium, while others can be hung externally. Additionally, they are  usually quite affordable. This flexibility is helpful if you’re just getting started with CO2 and don’t want to make a large equipment investment.

In-line CO2 Diffuser

In-line diffusers hook directly into canister filtration systems. They are powered via your filter’s motor, which pushes water through the diffuser. This means they usually can be hidden and reduce the clutter inside your aquarium, making your set-up more aesthetically pleasing.  However, they can be hard to calibrate, especially for larger tanks. They require a good filter flow rate and to operate well if used on the outflow line.

They are more efficient than the ceramic diffusers. However, they are not as effective as CO2 reactors. They are good choices for people who don’t like CO2 mist. 

The limitations of in-line diffusers are: 

  • Hard to install 
  • Harder to regulate 
  • Don’t work with HOB filters

Airstone Diffuser

Airstone CO2 diffusers are the same coarse stones used to increase water oxygenation in a tank. However, they are not very efficient. Better to keep the airstones with air pumps.

Do you need a CO2 diffuser?

If you want the most lush, densely planted tank of your dreams, then yes, you need a carbon injection system and CO2 diffuser. Plants need carbon dioxide in order to produce their own food and thrive. Plants like Anubias can survive with CO2 diffusers but they will definitely grow faster with the addition to their tanks.

If you run your injection into your aquarium without a diffuser, then you’re basically wasting the money you spent on the injection system. The large bubbles will float straight up and release your precious CO2 into the air. This completely misses the point. 

How to choose the best CO2 diffuser for your aquarium

Tank Size

Size matters. Simply put, a diffuser that is designed for a 10 gallon tank will struggle with your 55 gallon tank. There won’t be enough bubbles or pressure.

It is important to get a diffuser that is the appropriate size for your tank.

Ideal Type of Diffuser for Your Set Up

The ideal diffuser will depend on the type of carbon generator and regulator you’re using. For example, if you’re using pressurized CO2 cartridges, you’ll need a diffuser designed for high-pressure CO2.

co2 diffuser set-up

Additionally, if you’re using an in-line diffuser, be sure to check your filter supports a specific amount of flow. You need this flow level to push CO2 through the membrane to make microbubbles. If your flow is too low, no bubbles for you.

Construction and Material

CO2 diffusers have to be cleaned and maintained on a regular schedule. Minerals in your water can build up on ceramic disks. Algae can build up and block air flow. If you get a block in your line, it could stop the flow of carbon dioxide and thereby cut off the supply to your plants. In other words, you want your diffuser to be easy to clean.

Glass is the most common material for diffusers. Stainless steel is also becoming more popular. Glass is fragile but stainless steel is more durable.

Kit Inclusions

Kit inclusions can be a deciding factor for CO2 diffusers. Some diffusers come with additional equipment included, like U-bends, bubble counters, and check valves.

If you’re basing your decision on price, it’s important to understand if you need to buy additional pieces of equipment. Most of the additional pieces of equipment aren’t too expensive but again, knowledge is power.

Best CO2 Diffuser options:

Now you’re educated on CO2 diffusers, let’s explore different options to find the best CO2 diffuser for your situation.

Our all-around recommendation: Fibst CO2 Diffuser

This CO2 diffuser can generate all-round bubbles. You might think all bubbles are naturally round, but that is not always the case. Round bubbles are superior to partial bubbles for CO2 dispersion.

This diffuser is made of stainless steel, making it both easy to clean and not as fragile as glass. 

In this kit, you also get a 6-month warranty for the ceramic sheet, a 24-month warranty for other parts, and friendly customer service.


  • Stainless steel 
  • Needs 7.5PSI/0.5MPa air pressure to generate bubbles
  • Simple, elegant design


  • Easy to clean
  • Sturdy construction
  • Fine bubbles generated
  • Easy to replace ceramic disk


  • No bubble counter or check valve
  • Does not work well with DIY CO2 generator
  • Height is not adjustable

Jardli Pollen Glass CO2 Diffuser With Bubble Counter

This small glass diffuser from Jardli has a ceramic membrane that produces a fine mist of bubbles. This diffuser has a simple design and sits inside your tank. It comes complete with a built-in bubble counter.

The main downside is that this diffuser is made of glass. Given that you have to remove the diffuser from the tank for cleaning, you have to be careful when moving this piece of equipment.  You also can’t replace the ceramic disk.


  • Built in bubble counter
  • Ceramic disk permanently attached to glass
  • Designed for tanks below 20 gallons


  • Efficient- Bowl style CO2 diffusers dissolve up to 98% of the CO2 
  • Attractive design
  • Easy to clean


  • Fragile
  • Not recommended for low-pressure or DIY CO2 generators

JARDLI Glass Inline CO2 Atomizer Diffuser System

This diffuser from Jardli is a great inline option. The diffuser hooks into your canister filtration system, so you don’t have to clutter your tank. It works with any canister filters that use 0.5-inch wide tubing. 

To adjust CO2 levels, simply adjust your filter’s flow rate and the amount of CO2 entering the line. 


  • Hooks into canister filter system
  • Works best with pressurized CO2 systems


  • Works well for tanks of any size
  • Attractive design
  • Efficient CO2 dispersion
  • Good customer service


  • Fragile – some users reported easily broken glass
  • Does not include check valve
  • No bubble counter

Fluval Ceramic CO2 Diffuser for Planted Aquariums

The Fluval Ceramic Diffuser is extremely simple. It has a round plastic body around a ceramic disk so it looks like a black donut. It can be easily attached to the side of the tank with a suction cup.

It is easy to install and won’t break easily; however, it is not very attractive. We recommend hiding in the back of your tank behind a plant.  


  • Simple design with a tough plastic construction
  • Meant for smaller aquariums, 20 gallons or less


  • Can install anywhere with suction cup
  • Affordable
  • Easy to hide


  • Susceptible to clogging
  • Some users report suction cup stops working over time

Sera Flore Active CO2 Reactor 500 – Small 66-160 Gal

This model from Sera is top-of-the-line. It works with both pressurized and low-pressure CO2 injectors. 

The Sera can be installed in-line as part of your canister filtration system, or you can use it with a pump right inside your aquarium. 

CO2 reactors are substantially more efficient than your other options, so if you’re shooting for high-efficiency, a reactor is the way to go. Installation can be tricky but Sera has excellent customer service.


  • Diffuses up to 500 CO2 bubbles per minute 


  • Can be mounted internally or externally, depending on your tank
  • Most efficient bubble delivery system


  • Expensive
  • Noisy at the beginning as bubbles begin to diffuse
  • Some users report brackets breaking


The Twinstar CO2 diffuser uses ceramic stone to produce super fine bubbles, increasing CO2 availability to your plants. It is made of transparent acrylic, which is not as easily broken as some materials like cheaper plastics or glass.

 Various sizes available (Small, Medium, Large) are available for tanks up to 65 gallon.


  • Acrylic construction is more durable than glass
  • Ceramic stone and acrylic bonding technologies –  durable enough to withstand high pressure.
  • Suction cup makes it easy to move around your tank


  • Affordable
  • Ultra-fine bubbles good for CO2 dispersion


  • Reports of suction cup failing to hold grip
  • Some reports of large bubbles leaking out. Item not properly sealed.

CO2 Diffuser FAQs 

Where should CO2 diffuser be placed in aquarium?

Placement in the tank is important. The Diffuser should be placed in the bottom of the tank; you want to give the bubbles as much time as possible to diffuse before reaching the surface and breaking. 

​Can you use a CO2 diffuser with an air pump?

Using a CO2 diffuser with an air pump won’t create ultra-fine oxygen bubbles. The pressure from the air pump will not be sufficient to create the bubbles. 

Additionally, CO2 diffusers and air pumps often have different goals. 

With CO2, you want small bubbles that will rise slowly on their own to the top of the tank. This gives the maximum amount of time for the CO2 to get absorbed.

With air, you are generally trying to get water movement, so you want larger bubbles, which move more water. These are conflicting goals.

Can CO2 harm fish?

Too much CO2 can suffocate your fish. It will result in them coming to the surface and gulping for air. They will tend to hang around the surface because that is where the most remaining oxygen will be concentrated. If left unchecked, it can kill your fish. You want to avoid levels of CO2 above 30 PPM.


CO2 diffusers are a critical piece of equipment in planted tanks. They are integral to converting large CO2 bubbles into microbubbles which make the carbon more easily digestible by your plants. They help your CO2 injection systems work much more efficiently.

Our all-around recommendation for the best CO2 diffuser is the Fibst CO2 Diffuser. It is durable stainless steel with an elegant design. Depending on your tank size, it is a great option.

Do you use CO2 in your tank? What is your favorite CO2 diffuser?

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