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    Choosing the right CO2 diffusor

    A selection guide

    Carbon in the form of carbon dioxide (CO2) is one of the most important nutrients for a healthy growth of aquatic plants. Ideally the aquarium gets supplied with carbon dioxide via a CO2-system. The diffuser plays a big part in this. So called diffusors are particularly efficient here, since they atomize the CO2 in many, many tiny bubbles and facilitate the solution of the gas in the aquarium’s water. For this, the CO2 is pressed through a membrane made of ceramics with appropriate pressure. There are many different models and designs available.

    We will help you find the right CO2-diffuser for your aquarium.

    Aqua Rebell CO2 Diffuser small


    First of all, it is significant what type of CO2-system is used. Fundamentally you distinguish between systems using compressed gas (with disposable or reusable bottles) and bio-CO2. Due to operational reasons, the latter do not have a particularly high pressure, which can also fluctuate greatly. Many diffusers need a higher, constant CO2 pressure in order to work optimally. For this reason, low-pressure feedable diffusers are recommended for Bio-CO2 systems. We recommend the Air diffusors made by Neo Aquario. These are made of acrylic glass, quiet and offer a lot of value for money.

    AQUARIO - Neo Air Diffuser - U Type - Large

    Systems using pressurized gas offer a more constant performance and higher pressure. This will open up a much wider selection and you may choose a diffusor needing higher working pressure such as bigger glass- and steel diffusors or Inline Atomizers.

    Tank size

    The total water volume of the aquarium certainly has the most influence on the choice of CO2 components. This is based on the gross volume of the aquarium. The larger a pool is, the larger should the diffuser and the diameter of its ceramic membrane be. The CO2 system should work with a correspondingly higher pressure.

    Smaller-sized diffusers are more than enough for nano aquariums.Furthermore, such small tanks can be operated well with a Bio-CO2 system. The UP Aqua mini diffuser is especially small and nice to look at.

    In aquariums with a larger volume (500 liters upwards) or with an appropriate edge length (1.50 meters upwards), it can make sense to use two diffusers. These are installed on the left and right side of the aquarium and ensure a better CO2 distribution.

    Glass, acrylics or steel?

    If you use filter inlets and outlets (Lily Pipes) made of glass or stainless steel in your aquascape or planted tank, you may also use the same materials when it comes to CO2 tech. Many diffusers and hose connectors (J- or U-pipes) are available in glass or stainless steel variants. The former usually have very fine-pored membranes, which, depending on the model, often are replaceable. This facilitates cleaning and repairs.

    Aqua Rebell - CO2 Diffuser - BowlAquasabi - CO2 Diffuser - stainless steel Pollen - 25

    Our online store also offers diffusers made of acrylics or plastic. They have the benefit of a low price and often come with excellent, fine-pored membranes. These ensure (at an appropriate working pressure of usually 2 bars or more) the formation of really extremely small bubbles and thus an excellent solubility of the gas in the water. Models made of acrylics are also visually appealing, whereas coloured plastic models might be more visually striking.

    Borneo Wild - CO2 Power Atomizer

    The Borneo Wild CO2 Power Atomizer produces micro-sized bubbles.

    Invisible CO2 technology

    Inline-diffusers are an interesting solution for larger aquariums but also for more puristic acuascaping layouts where as little technology as possible is supposed to be seen. These are installed, hidden in the bottom cabinet of the aquarium between filter pot and outlet in the hose section of the external filter.

    Up Inline Atomizer

    Inline-diffusers are available for all usual hose diameters and hardly influence the flow rate. The atomization of gas is even finer in these models and they are very quiet. But a higher working pressure is needed in order for the Inline Atomizer to operate correctly. We recommend a pressure of 1,8 bar.

    Only microfine CO2 bubbles, which have been flushed into the tank from the filter outlet are visible in this type of feed. (see video).

    Quality of ceramic membranes

    The quality of the membrane also influences the CO2 solubility in the aquarium water. The more porous a membrane is, the better it can produce micro-fine bubbles. Smaller CO2 bubbles have a larger surface-to-volume ratio than larger bubbles. Thus, the gas can dissolve faster in the water (see also: Sukei Research). However, this also requires a higher working pressure in the CO2 system (often 2 bar). The aquarist should make sure that the components of the system such as pressure reducer, hose and check valve are designed for such high pressure.

    Above all, many diffusers made of acrylic glass, plastic or stainless steel and Inline Atomizers as well as higher quality glassware from ADA or Aqua Rebel are equipped with very fine-pored membranes. Due to this, we have made an overview of the appropriate diffusers for typical aquarium sizes. The suggestions for the respective volume of the aquarium are summarized in a ranking list sorted by recommendability:

    Overview: CO2 diffusers

    20 to 30 l nano aquarium, Dennerle Scaper's Tank 35 l or Nano Cube, ADA Mini M:

    54 l Standard aquarium (60x30x30 cm), Dennerle Scaper's Tank 50 l or ADA 60-P:

    112 l Standard aquarium (80x35x40 cm):

    182 l Standard aquarium (90x45x45 cm), ADA 90-P:

    250 l Standard aquarium (100x50x50 cm) or 243 l ADA 120-P:

    350 to 500 l aquarium: