Understanding CO2 in Nature Aquariums

Providing injected CO2 underwater is the key to successful Nature Aquariums. Like terrestrial plants, underwater plants breathe in CO2 and exhale oxygen during photosynthesis. In nature, CO2 is introduced into the ecosystem because of acidic water (low pH) from decaying vegetation, and from dissolving minerals from stones in the landscape. However, in a Nature Aquarium environment, there isn’t the same degree of plant decay or dissolved minerals, so Takashi Amano introduced the concept of injecting CO2 to allow plants to flourish underwater.

CO2 is injected only when the lights are turned on, as this is when photosynthesis takes place and is the only time that plants will need to breathe in underwater CO2. CO2 should be turned off when the lights are, because in the dark plants start to breathe oxygen instead of CO2. This depletes the aquarium of oxygen that the fish require.

Just the right amount of CO2 is needed. A good oxygen/CO2 ratio is a must to keep both fish and plants thriving in aquariums. If you see fish gasping for air, that means there is an insufficient supply of oxygen and too much CO2. On the other hand, if not enough CO2 is injected into the system, plants will not be able to photosynthesize properly.


CO2 Systems

With ADA’s CO2 systems, CO2 gas is compressed and stored in steel cartridges or tanks, just like oxygen is stored in tanks for medical use. There are two options when choosing your CO2 delivery method: cartridges or towers.

ADA CO2 System 74 Cartridges

These small cartridges are a convenient way of providing injected CO2. They are designed for use with small tanks (30cm to 60cm) and are easily replaceable so there is no need to find refilling stations for CO2 tanks.

Each ADA CO2 cartridge contains 74 grams of compressed CO2. The cartridge will last approximately four weeks (injected at a rate of one bubble/second for eight hours a day).

They are used together with CO2 System 74-YA or CO2 System 74-SA Regulators.  Even beginners can easily attach the cartridge to the regulator.

The CO2 cartridge is infused with fragrances inspired by the world’s three major tropical rainforests: Amazonia, Malaya, or Africana.

ADA CO2 Tower

CO2 Towers are the most economical choice for large Nature Aquarium systems, and can also be used for small tanks. Each tower contains a steel CO2 tank with a capacity of 18 ADA System 74 Cartridges (or 1.332 kg of compressed CO2), encased in an elegant outer stainless steel sleeve. Since the right amount of CO2 is essential for the health of both the fish and plants, it is important that CO2 injection remains as constant as possible. However, ambient temperature during the height of summer may affect the pressure inside the CO2 tank and alter the CO2 injection supply. The ADA tower casing is not only attractive, but also acts as an insulator to controls temperature fluctuations. For a 170-litre Nature Aquarium tank, it will take approximately six months before the next refill is needed.


Additional Equipment

ADA CO2 Regulators

Regulators reduce the high pressure of compressed CO2 to a manageable low-pressure output. This will make it easy for you to inject just the right amount of CO2 into your Nature Aquarium. You measure the CO2 by counting the number of bubbles per second using a bubble counter. ADA CO2 Regulators have user-friendly needle valves, making it easy to adjust the number of bubbles per second.

There are two types of ADA regulators:

ADA CO2 System 74-YA is the basic regulator for CO2 cartridges. You will need to adjust the needle valve from time to time as the cartridge loses pressure.

ADA CO2 System 74-SA is the high-grade model regulator for CO2 cartridges. It comes with a gauge that allows you to precisely control the discharge pressure without adjusting the needle valve. This feature appeals to Nature Aquarium owners who want to regulate the number of bubbles per second easily and fast.


When CO2 diffusers are not cleaned regularly, they will start to clog, causing extreme pressure inside the CO2 tubings. Both ADA regulators have a safety valve that will release CO2 if pressure builds up in the tubing. It will also prevent excessive CO2 from being injected into the Nature Aquarium. Other CO2 regulators do not offer this kind of safety system.

ADA CO2 Adapter

A precision-machined adapter that allows you to upgrade from using System 74 Cartridges to the large ADA CO2 Tower. Many Nature Aquarium owners with small tanks start by using cartridges and later upgrade to the ADA CO2 Tower when they have a bigger tank. By simply adding this adapter, you can continue to use the same ADA regulator that you purchased for System 74 Cartridges.

If you have decided to purchase an ADA regulator that will be connected to a large North American CGA-320 CO2 tank, you can simply buy the ADA CO2 Attache Regulator (ADA CO2 System 74-YA plus ADA Regulator Adapter) or the ADA CO2 Speed Regulator (ADA CO2 System 74-SA plus ADA Regulator Adapter). This is more cost-effective than buying them separately.

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ADA Speed Regulator                        ADA Attache Regulator

ADA CO2 Glass Bubble Counter

Provides an easy way to know how much CO2 is being injected into the Nature Aquarium. Too much CO2 will kill fish, while too little provides no benefit for the plants. ADA offers two bubble counters: the ADA Glass Counter and the ADA Beetle Bubble Counter. In both cases, water is filled inside the vial and gas bubbles can then be counted as they rise through the water. Count the number of bubbles produced over ten seconds and then divide the number by ten to get the number of bubbles per second.


CO2 Diffuser

Underwater plants breathe in CO2 in liquid form. CO2 gas should be diffused into very small bubbles in order for it to be absorbed by the water and converted into a liquid state. ADA CO2 Diffusers are made of powdered glass, which produces very tiny bubbles that gets absorbed into the water efficiently.

Choose the correct diffuser based on the size of your aquarium. Using a too-small diffuser will not introduce sufficient CO2.



The chart below shows the complete list of ADA CO2 Diffuser sizes:


Tank Size

ADA Diffuser

60x30x36 cm Pollen Glass
60x30x36 cm Pollen Glass Type-2
60x30x36 cm Pollen Glass Type-3
60x30x36 cm Pollen Glass Large 20Ø
60x30x36 cm New Pollen Glass
30x18x24 – 36x22x26 cm Pollen Glass Mini
75x45x45 – 90x45x45 cm Pollen Glass Large 30Ø
75x45x45 – 90x45x45 cm Pollen Glass Beetle 30Ø
90x45x45 – 120x45x45 cm Pollen Glass Beetle 40Ø
120x45x45 – 180x60x60 cm Pollen Glass Beetle 50Ø


ADA Cabochon Ruby or Check Valve

When CO2 pressure drops or when the electronic solenoid shuts off CO2 supply, the CO2 hose becomes a natural siphon that draws water from the main tank and into the regulator by gravity. Water will damage the CO2 regulator. The check valve allows CO2 to be injected in the Nature Aquarium system but will prevent water from flowing back. You can use the more sophisticated ADA Cabochon Ruby or an ordinary air line check valve for this purpose.


Pressure-Resistant Tubing

A special tubing used because ordinary tubing often breaks and causes leakage. Pressure-resistant tubing is very rigid and is used only to connect to the regulator “fast push-in” fitting and other durable plastic fittings (such as a plastic check valve). It is too stiff to be connected to glass – do not use with glass attachments such as CO2 diffusers or bubble counters.


CO2 Tubing

This softer tubing has a very good gas barrier property that prevents CO2 from escaping through its membrane. The tubing can be heated in hot water to further soften it and make it easier to connect to glass items such as the ADA CO2 Pollen Glass, ADA Glass Bubble Counter, etc. Use clear or grey according to your preference.

ADA EL Valve

An electronic solenoid valve that starts CO2 delivery into the Nature Aquarium when energized and shuts off CO2 when power is cut. The ADA EL Valve is meant to plug into the timer that controls the light, so that your CO2 system only turns on when the lights do. This is a convenient way of automatically starting and stopping the CO2: turning off CO2 injection when lights are off prevents excessive CO2 concentration that can harm your fish, and helps you conserve your CO2 supply.

ADA NA Timer

An automatic timer and solenoid valve combined in one. The timer provides precisely eight hours of light a day to simulate the correct photoperiod for plants. It comes with three “timer-controlled” outlets that operate two light sources and one air pump.  At the same time, the ADA NA Timer also has a built-in solenoid valve (ADA EL Valve) so it automatically starts or stops CO2 supply when the lights are turned on or off, respectively.

Plants do not need CO2 when lights are off; they actually start using oxygen. Now the plants and fish compete for oxygen in the system.   Insufficient oxygen will cause beneficial bacteria to die, increasing chances of having ammonia spikes which will lead to algae. Turning on an air pump to add oxygen when the lights and CO2 system are off is highly recommended. The ADA NA Timer comes with a third outlet that turns on when the first two turns off. This is usually attached to an air pump that adds oxygen to the Nature Aquarium automatically and removes excess CO2.

Joint Glass

The use of joint glass prevents CO2 tubing from kinking and stopping CO2 flow. Select the right ADA Joint Glass size depending on the thickness of the tank walls.


Complete CO2 systems with all the necessary equipment are available as package purchases. Your tank size will determine which is right for you.

The Do!Aqua Starter Kit is perfect for beginners with small Nature Aquariums (less than 40 litres). Here’s a short video explaining the components:

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You can also purchase the ADA Advanced System Kit. This kit is for intermediate users with Nature Aquariums up to 65 litres. See it in action:

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Click on the icon below to download ADA literature on CO2.

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