Every successful aquarium hobbyists know that plants that are supplied with enough CO2 and lighting grow much more gorgeously than those without using an external CO2 supplier. However, there are a lot of equipment needed for setting up a CO2 supply system that makes beginners frustrated. These include CO2 regulator, CO2 cartridge, bubble counter, diffuser, etc. The real is that everything is very easy if you can understand the fundamental of a CO2 system. Don’t worry, this guide includes everything you need for setting up a CO2 supply system for your planted aquarium.

How a CO2 supply system works?


The fundamental of a planted tank CO2 supply system is fair easy to understand. High pressure CO2 from a CO2 cartridge (CO2 canister) goes through a CO2 regulator to lower its pressure and make it suitable for using in the planted tank. Besides, the CO2 system also includes other supplies needed to convert CO2 gas into a large number of fine bubbles that are easier to dissolve in the aquarium water. Finally aquatic plants use CO2 in the water for synthesizing nutrients they need for life (photosynthesis procedure).

The pressurized CO2 system with regulator works well because you can adjust the pressure to achieve your desired flow rate of CO2 gas into your aquarium. An advanced regulator with a timer and a solenoid valve can help you turn off the system at night (aquatic plants do not use CO2 at night) that saves the CO2 as well as your money. The timer helps to control when the electric is turned on or off and the solenoid valve will open only if the electric is turned on that allows CO2 go through the regulator.

There are also a method using yeast to produce CO2 instead of buying the CO2 cartridge; however, the system with pressurized cartridge will be cheaper than the yeast-based system on the long run and you can expect much better results. It’s 100% stable and you only need to refill the cartridge once every 6 to 12 months (depending on tank size, planting density, etc). That kind of system is expensive initially but it’s worth the money invested.

Structure of a CO2 regulator for planted tank

A CO2 regulator is used to control the amount of CO2 that is added to your aquarium. The regulator works by attaching to a CO2 canister and allowing a measured amount of CO2 into your tank at a measured flow rate.


Most CO2 regulators have a similar structure, with high and low pressure gauges, a bubble counter, a needle valve, and a solenoid valve. Some regulators will only have a single gauge (the low pressure gauge), and others will not have a built-in bubble counter. This can be added farther along the tubing.

The high pressure gauge measures the amount of pressure in the CO2 cylinder. It tells you whether or not there is liquid CO2 remaining in the tank, but does not tell you how much CO2 there is left. When the high pressure gauge reads zero (or low) it is time to replace your CO2 cylinder.

The low pressure gauge measures the pressure of CO2 that is being used. The amount of pressure being released into the aquarium can be adjusted. A low pressure gauge gives a measure of the output pressure which has been reduced from the cylinder’s pressure; maximum values are often between 150 and 200 psi.

The bubble counter allows you to estimate the rate of flow of CO2 into your aquarium by providing a bubbles per second count. It is a visual representation of the flow rate which can be adjusted with the needle valve.

The needle valve controls how much CO2 is released from the cylinder into the aquarium. It can be adjusted to set the flow rate (bubbles per second) on a very fine scale. The precision of the needle depends on the regulator quality.

The solenoid valve acts as an on/off switch for the CO2 regulator. It can be connected to a timer so that the regulator is only adding CO2 during specific times. It can also be connected to a pH meter and set up to shut off the regulator if the pH of the aquarium falls outside of an optimal range.

Best CO2 regulator and CO2 supply kit for planted tank

Pro CO2 Mini CO2 Regulator with dual gauges and selenoid valve

Pro CO2 Mini CO2 RegulatorEditor's rating: Check on

The Pro CO2 mini regulator is a dual gauge regulator that comes with a bubble counter, check valve, and 110V solenoid. It fits standard US CO2 cylinders, and is compatible with most standard aquarium tubing, atomizers, and diffusers. The precision valve allows for fine tuning of the CO2 flow rate, while the bubble counter allows the exact flow rate to be visualized. The CO2 regulator will work with a cylinder pressure up to 2000 psi, and allows for output pressures up to 150 psi.

S.T. International Aquarium 2-Gauge Professional CO2 Regulator

S.T. International Aquarium CO2 RegulatorEditor's rating: Check on

The S. T. International regulator is a dual gauge regulator with a patented solenoid magnetic valve. The solenoid is designed to use with universal voltage (110V and 220V) for worldwide use. The regulator can be used with standard US CO2 cylinders or with disposable cylinders. The package doesn’t include a check valve, a bubble counter and a diffuser, so you need to buy these supplies buy yourself to fulfill the setup.

Up Aqua CO2 regulator with 2 gauges and adjustable valve

Up Aqua CO2 regulatorEditor's rating: Check on

The U. P. Aqua CO2 regulator is a dual gauge regulator with adjustable working pressure. The gauge units are available in psi and kg/cm3. It is compatible with standard US CO2 cylinders (CGA320 connector). The regulator has a high precision needle valve to adjust flow rate, and an electronic solenoid rated at 110V.

AQUATEK CO2 Regulator Mini for paintball CO2 tank

AQUATEK CO2 Regulator MiniEditor's rating: Check on

The Aquatek Mini is designed for use with paintball CO2 tanks (buy separately). It consists of a dual gauge, cool-touch solenoid, and precision needle valve. It also comes with a bubble counter with integrated check valve. The system is compatible with most CO2 atomizers and diffusers. This CO2 regulator works with cylinder pressures under 1500 psi, and allows for output pressures up to 200 psi. The solenoid has a dual voltage design (110V and 220V).

Fluval Pressurized 88g-CO2 kit for 15-40 gallon planted tanks

Fluval Pressurized 88g-CO2 KitEditor's rating: Check on

The Fluval Pressurized 88g-CO2 kit is designed to be used with 88g Fluval disposable CO2 cylinders. It is designed for small to medium sized planted aquariums from 15 to 40 US gallons. The kit comes with a single regulator gauge with needle valve, a disposable CO2 cylinder, a bubble counter, a ceramic diffuser, hosing, and a holding bracket.

Fluval Mini Pressurized 20g-CO2 kit for nano planted tank up to 15 gallons

Fluval Mini Pressurized 20g-CO2 kitEditor's rating: Check on

The Fluval Mini Pressurized 20g-CO2 kit is designed to be used with 20g Fluval disposable CO2 cylinders. It is designed for nano to small sized planted tanks up to 15 gallons. The kit comes with a single-gauge regulator with regulator valve, a disposable CO2 cylinder with bracket, an internal CO2 diffuser, and hosing.

Other supplies for planted tank CO2 systems

CO2 bubble counter

Glass CO2 Regulator Bubble CounterGlass CO2 Regulator Bubble Counter Fluval CO2 Bubble CounterFluval CO2 Bubble Counter

A CO2 bubble counter is a very helpful equipment for planted tanks. It helps to estimate the amount of CO2 is injected into your planted aquarium and is measured by the number of bubbles per second. By using this tool combined with a CO2 drop checker, you can know exactly if the CO2 levels in your planted aquarium are in your desired range or not. Most CO2 regulators on the market today are already included a bubble counter and you don’t need to buy an external one.

Check valve

Rhinox CO2 check valveRhinox CO2 check valve

A check valve is to prevent back flow of tank water towards the CO2 regulator side. As CO2 easily dissolves in water, the tank water enters the tube after the CO2 injection is stopped. If it is left untreated, the tank water even reaches the CO2 regulator which may cause a malfunction. In some CO2 regulators, the check valve is already included and you don’t need to buy it separately.

CO2 diffuser

Pollen Glass CO2 DiffuserPollen Glass CO2 Diffuser

CO2 gas from the CO2 supplier (CO2 regulator and cartridge) need to be converted to tiny bubbles to enhance its dissolving efficiency. A good CO2 diffuser with its very small pores will proceed this procedure. You will need a diffuser that has the size fit your aquarium size. The best CO2 diffuser is one that can convert CO2 into fine bubbles, the smaller bubbles it converts the better.

With the diffuser, CO2 is converted into fine bubbles, which move slowly then rapidly dissolve in water and are distributed throughout the planted tank. Without a CO2 diffuser, large CO2 bubbles are produced and escape the water easily, and not or very little diffuse in your aquarium.

How to set up a CO2 supply system for a planted aquarium?

After buying all equipment you need for setting up your CO2 supply system, you can assemble them follow an order that starts from the cartridge and completes with the diffuser.

CO2 cartridge –> regulator –> bubble counter –> check valve –> diffuser


Step 1: Attach the CO2 regulator to the cartridge. Don’t worry! almost regulators are designed to perfectly fit with CO2 cartridges sold on the market today and you don’t have to buy any adaptor to connect them. Sometime, a CO2 paintball adapter will add some help.

Step 2:  Using appropriate CO2 air-line tubing to connect the air outlet from the regulator with a check valve and then with a diffuser. If your CO2 regulator isn’t equipped with a bubble counter, you can buy one and connect it with the air outlet from the regulator. The diffuser is placed in the back end of the system where CO2 is converted into fine bubbles which are then injected in the aquarium water.

Step 3: Placing the diffuser in a proper place in your aquarium, where has a good water circulation, by using suction cups.

Step 4: Set up a CO2 drop checker and place it inside the planted aquarium with a suction cup. This equipment helps to read the fairly exact CO2 concentration in your planted tank. By adjusting the regulator combined with using a CO2 drop checker, you can get an optimal CO2 concentration in your planted tank. The recommended level of CO2 for a planted tank is approximately 26-35 ppm.

What happens if the CO2 levels are too low/high?

Plants require CO2 for photosynthesis. This is a fundamental process where plants convert CO2 and water, in the presence of light, into oxygen and sugar. These sugars are required for plant growth and the production of new roots, stems, and leaves.

In an aquarium there will be a small amount of CO2 present in the water from the environment, and a slightly greater amount if there are fish or other animals in the aquarium as they produce CO2, but in order for plants to flourish additional CO2 is required. If the level of CO2 in a tank is too low, plants will not grow. They will begin to show signs of yellowing, be stunted, and may eventually die, depending on the species.


Deficiency of CO2 in aquarium plants. Image by Xiaoxiy,

Another potential problem with low CO2 levels is the increased risk of algae and algal blooms. This is because algae can thrive at much lower CO2 levels than most aquarium plants, especially in high light levels and when other water conditions are imbalanced. High levels of algae can result in plant deaths, and can lead to anoxia in the water and high levels of ammonia which can be fatal to animal inhabitants.

CO2 also plays a role in regulating the pH of a tank. If the CO2 level in an aquarium is too low it may lead to an increased pH. In contrast, if the CO2 level is too high it can lead to acidification.

If CO2 is supplied too much in your planted tank, you may encounter problems with the health of your fish and invertebrates due to lack of oxygen. For this reason, a COregulator should be used to maintain aquarium CO2 levels within an optimal range. To maintain the CO2 concentration in this optimal range, you need to use a bubble counter and a CO2 drop checker test kit. Continue to read these following guides.

Using a CO2 bubble counter – How many bubbles per second?

The adequate amount of CO2 to be supplied varies depending on your tank size. This is because a larger amount of CO2 is required for a large amount of water to maintain the same CO2 level. Even for the same size of aquarium, the appropriate amount of CO2 varies with the type and thickness of aquatic plants growing in it. Therefore, it is necessary to finely control the amount of CO2 to be supplied for each tank. The ideal tools for the adjustment of the CO2 levels are the CO2 bubble counter.


A bubble formed inside the CO2 Bubble Counter. It refers to the amount of CO2 injection.

During the initial setup period of aquarium, the amount of CO2 should basically be about one third to one half of the volume indicated in the aquascape data. Basically, you should start CO2 supply at one bubble per second and then gradually increase the amount in line with the growing speed of aquatic plants.

For example, the standard amount of CO2 to be supplied to a 20 gallon aquarium is “one bubble per second with CO2 bubble counter” in its initial stage. As the aquarium ages, the CO2 amount is to be gradually increased to cope with a higher rate of photosynthesis of growing aquatic plants. When you have trimmed the plants to half their height, you should reduce the CO2 supply amount to half.

Keep in mind that excessive CO2 amount can contribute to slower leg movement of Amano shrimps (Caridina Japonica) due to a minor lack of oxygen. In this event, the amount of CO2 supply should be slightly reduced to adjust to the appropriate amount. This adjustment method is effective to find the optimal amount of CO2 to be supplied; but it requires a certain amount of experience.

Using a CO2 drop checker – How much CO2 for planted tank?


A CO2 drop checker test kit helps you to monitor the change of CO2 level in the water by the change in color of its pH reagent ranging from blue, to greenish yellow, to yellow. The pH level of water changes by how much CO2 is supplied to the aquarium.

Based on this fact, Drop Checker, which changes its reagent color according to the pH level of water helps you determine if the CO2 supply amount is appropriate. It can be determined that an appropriate amount of CO2 is supplied if the reagent has turned green in a few hours after the CO2 supply is started (and the lighting is turned on). In the event the reagent remains blue, the CO2 amount is too little while it is too much if the reagent turned yellow.

  • A healthy aquarium should have a CO2 level of anywhere between 20 to 40 ppm (part per million). 30 ppm is an ideal level for both plants and fish.
  • A blue color indicates you have a CO2 level of 25 ppm or less.
  • A green color indicates your have a CO2 level of 26-35 ppm. It is ideal if your checker changes to the green color.
  • A yellow color indicates you have a CO2 level of 36 ppm or more.

A CO2 Drop Checker kit is very cheap, helpful and easy to use; you can read my full guide to use a Drop Checker here:

Leave a Reply

Your email address will not be published. Required fields are marked *