A lot of equipment is used in setting up a CO2 supply system for planted aquarium such as CO2 regulator, cartridge, diffuser… which you might find a little complicated initially. Please don’t worry because the setup will be relatively simple after you read this guide.

There are three main compartments of a normal CO2 injection system, they include:

  • CO2 cartridge: filled with a high-pressure liquid CO2 that provide CO2 gas for the system.
  • CO2 regulator: to reduce the pressure and release CO2 from the cartridge. The regulator includes valves to control the amount of CO2 injection into your aquarium.
  • CO2 diffuser: converts CO2 gas from the regulator into fine bubbles enhancing the dissolved CO2 that is kept in the water and ready for aquatic plants to use.

A complete CO2 supply system will look like this:

CO2 supply system. Image sourceCO2 supply system. Image source

Let’s look at the configuration of these equipment to understand how it works.

CO2 regulator and cartridge – main CO2 supply section

The CO2 cartridge (CO2 pressurized cylinder) is filled with a high-pressure liquid CO2. To reduce the pressure and release CO2 from the cartridge, a piece of equipment called the CO2 regulator is required. These small CO2 cartridges and CO2 regulators serve as the source of CO2 supply. The pressurized CO2 system with regulator works well because you can adjust the pressure to achieve the desired flow rate.

aquarium CO2 regulatorEditor's rating: Check on Amazon.com

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.

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.

CO2 diffuser and other outlet section equiment

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 it is. Following is an affordable diffuser you can buy.

Rhinox Nano CO2 diffuserRhinox Nano CO2 diffuser

With the diffuser, CO2 is converted into fine bubbles, which move slowly then rapidly dissolve in water and are dispersed across the tank. Without a CO2 diffuser, large CO2 bubbles are produced instead of tiny ones that escape the water easily, and not or very little diffuse in your aquarium.

Along with the CO2 diffuser, the CO2 outlet section also consists of bubbles counter and check valve ensuring that CO2 is converted into your planted aquarium in the proper way.

Rhinox Brass Bubble CounterRhinox Brass Bubble Counter Fluval CO2 Bubble CounterFluval CO2 Bubble Counter Rhinox CO2 check valveRhinox CO2 check valve

Many aquarists love to use a CO2 bubble counter in their CO2 system because most the aquascapes published online today come with the parameter measured by the number of bubbles per second to maintain the healthy plants in each aquascape. With the bubble counter, you can precisely know the CO2 injection that follows the aquascape you want to set up, even if you are a beginner. If your CO2 regulator has already included a bubble counter, you don’t need to buy it separately.

The check valve is a part 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 advanced system, the check valve is included and you don’t need to buy it separately.

Best CO2 regulator and CO2 supply kit for planted tank

AQUATEK CO2 Regulator Mini with solenoid valve for paintball CO2 tank

  • Editor's rating: Check on Amazon.com
  • Designed to perfectly fit paintball CO2 tank without using any adapter
  • There are two gauge pressure indicators, one for CO2 tank pressure (1,500 psi max) and one for working pressure (200 psi max)
  • Adjustment knob for control of the CO2 injection pressure
  • Precision needle valve for fine tuning release of CO2
  • A solenoid valve used for electrically turn on/off the CO2 injection
  • A bubble counter and check valve are also included and you don’t need to buy them separately.
  • Editor's rating: Check on Amazon.com
  • Note: Paintball tank is NOT included
  • You can buy the regulator only or buy it along with a recommended CO2 tank and a CO2 tubing 16-feet used for hosing.

Up Aqua CO2 regulator with 2 gauges and adjustable valve

  • Editor's rating: Check on Amazon.com
  • Like the previous, it has two gauges measured for CO2 tank and working pressure
  • The gauge units are available in psi and kg/cm3
  • Designed to fit almost CO2 tank
  • An adjustable valve allows to control the working pressure
  • The valve is paired with high precision needle valve for accurate dosing
  • An electronic solenoid is also included for convenient use.

Premium AQUATEK CO2 regulator with integrated solenoid

  • Premium AQUATEK CO2 regulatorEditor's rating: Check on Amazon.com
  • Compatible with most high density tubing
  • Comes with two gauges (in both psi and kg/cm3)
  • Adjustment knob allows to adjust the output working pressure up to 140 psi
  • Includes solenoid valve and precision needle valve
  • A bubble counter and check valve are also included and you don’t need to buy them separately.

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

  • Fluval Mini Pressurized 20g-CO2 kitEditor's rating: Check on Amazon.com
  • Includes a disposable 20g CO2 cartridge with its bracket
  • Regulator valve controls CO2 output
  • Ideal for small starter planted aquariums up to 15 gallons
  • Some other supplies such as hose, diffuser ready for the setup.

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

  • Fluval Pressurized 88g-CO2 KitEditor's rating: Check on Amazon.com
  • Includes a disposable 88g CO2 cartridge with its bracket
  • A regulator valve with gauge for the effective control of CO2 output
  • Ideal for a 15-40 gallon planted aquarium
  • Some other supplies such as bubble counter, connection hosing, CO2 ceramic diffuser are also included.

Setting up a CO2 supply system for planted aquarium

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

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

Step 1: Assemble the CO2 regulator with 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.

CO2 paintball adapterCO2 paintball adapter CO2-proof tubing 16 feetCO2-proof tubing 16 feet

Step 2: Hosing the regulator outlet tube with other outlet section equipment using air-line tubes. If you use a bubble counter and/or a check valve in the system, connect them with the regulator and the diffuser by air tubes. The diffuser is placed in the end head of the system where CO2 is converted into fine bubbles and go through the aquarium water.

Step 3: Position the diffuser inside your aquarium by a suction cup.

Step 4 (optional): Set up a CO2 drop checker and place it inside the aquarium with a suction cup.

Control CO2 injection with bubble counter and drop checker

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.

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.


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

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.

If you are a beginner, it is recommended to use a Drop Checker for convenience. The CO2 Drop Checker helps you 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.


Reagent colors of the Drop Checker can be used as a reference of CO2 level in the water.

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: https://lovefishtank.com/co2-drop-checker-kit/.

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