How to Set Up a CO2 System for Planted Aquariums the Easy Way – Aquarium Co-Op


When it comes to planted tanks, we always encourage beginners to start with easy, slow-growing plants that only need low lighting and an all-in-one fertilizer. However, certain plants are a little more difficult to grow underwater and may require high lighting and extra carbon dioxide (CO2) beyond what is naturally provided in the air. When it comes to injecting CO2 gas into water, aquarists have tried all kinds of techniques, types of equipment, schedules, and dosage amounts to put together their own custom DIY systems. At Aquarium Co-Op, we have experimented with many of them and put together this basic guide to explain our favorite method that is reliable and easy to use.

Does CO2 get rid of algae? It’s a common belief that CO2 automatically fixes algae problems, but this is not true. A healthy planted tank must have three components in balance — lighting, fertilizer, and carbon dioxide. CO2 is just one of the primary nutrients that plants need to grow. Many beginners use too much light and fertilizer, so adding CO2 can help balance the aquarium. However, if a tank has high lighting and CO2 injection but, for example, too little fertilizer, then algae will appear because of the imbalance.

Let’s use a cookie recipe as an analogy. If you add 5x the usual amount of flour (e.g., fertilizer) to your dough, then you must also multiply the rest of the ingredients (e.g., lighting and CO2) by 5x, which will result in a bigger batch of cookies (e.g., greater plant growth). However, if you add 5x the amount of flour and then try to “balance” the recipe by only adding 5x the amount of chocolate chips (e.g., CO2), the rest of the ingredients are not in the correct ratio and will result in a bad cookie (e.g., algae growth).

Do all aquarium plants need CO2 injection? As mentioned before, all aquatic plants use CO2 as one of their basic building blocks. Some types like cryptocoryne plants do not need the extra CO2, while other plants like scarlet temple could benefit from it but don’t require it. A third category of plants — which includes Blyxa japonica, dwarf hairgrass, and dwarf baby tears and other similar carpeting plants — has higher demands and necessitates the use of CO2 for the best chances of success.

Materials for a CO2 System

In this guide, we are focusing on the installation of the CO2 system and not the lighting and fertilization components. To get started, gather the necessary equipment and tools:

Aquarium Co-Op diagram for CO2 system parts


  1. Aquarium Co-Op CO2 regulator

    • What is a regulator? A regulator is a device that allows you to precisely control how much gas exits the CO2 cylinder tank and enters the aquarium water.
    • What is the difference between a single-stage vs. two-stage regulator? A single-stage regulator reduces the cylinder’s gas pressure in one step, whereas a two-stage regulator reduces the pressure in two steps, resulting in a more stable and reliable flow of CO2. A two-stage regulator also helps to prevent “end-of-tank dumps,” in which a nearly empty CO2 cylinder may dump out the rest of its gas in one go.
    • Should I use a DIY CO2 or pressurized CO2 system? We have tested many types of DIY systems using yeast, citric acid, and other mixtures, and while they may be cheaper, they are not as stable as a pressurized CO2 system using a regulator and cylinder. The DIY reactions often make lots of CO2 at the beginning and then decline over time, and the inconsistent amounts of CO2 can make it difficult to balance a planted tank. Furthermore, the pressure is not as high, temperature can affect the reaction, and the overall process is time-consuming to maintain. With a pressurized system, we just set it up once and let it run for one to three years before having to refill the cylinder.
  1. Aquarium Co-Op manifold block add-ons (optional)

    • With our regulator, you can install up to five extra manifold blocks add-ons to expand the system and run CO2 to multiple tanks.
  1. CO2 cylinder tank
    • Can I use a CO2 paintball cylinder? No, the Aquarium Co-Op regulator is not intended for use with paintball tanks. They work with standard cylinder tanks that have the male thread size CGA320.
    • Where can I buy a CO2 cylinder? We like to get ours from local home brewing supply stores and welding supply stores. Usually, they also offer CO2 refill services if you bring back your cylinder when it’s empty.
    • What size CO2 cylinder should I get? If you are running a high tech planted aquarium injected with high amounts of CO2, people recommend getting the largest size possible so you will not have to refill the cylinder as frequently. However, for the average customer, we often suggest a 2.5–5 lb. cylinder for 20-gallon aquariums or smaller, a 5 lb. cylinder for 25- to 40-gallon aquariums, and a 10 lb. cylinder for 55-gallon aquariums or larger. If you plan on using one regulator with five or six aquariums, then scale the cylinder size accordingly.
  1. Airline tubing or CO2 tubing

    • Do I need to use special CO2 proof tubing or CO2 resistant tubing? We use the Aquarium Co-Op airline tubing (i.e., a flexible, black tubing made from food-grade PVC) on all of our aquariums and have not detected any perceptible loss of CO2. In our experience, special CO2 tubing is more expensive, harder to bend, and not as readily available.
  1. Regular check valve or stainless steel check valve (optional)

    • Do I need a check valve for my CO2 system? Check valves are used to prevent water from flowing out of the aquarium and pouring all over the regulator when it is turned off. The bubble counter in the Aquarium Co-Op regulator comes with a built-in check valve, but you can install a second one as backup if desired. We have personally used the regular plastic check valves with CO2 systems at our fish store, warehouse, and homes, and they have not broken down. That being said, CO2 does degrade plastic after a very long time, so we also offer a stainless steel version for greater durability.
  1. CO2 diffuser

    • Which type of diffuser should I get? Any CO2 diffuser intended for aquariums that can operate at approximately 40–50 psi should be fine.
    • How do I clean a CO2 diffuser if it becomes clogged? Diffusers must be cleaned or replaced at some point because of algae buildup. Because diffusers can be made of different materials, follow the manufacturer’s cleaning instructions to use diluted bleach, vinegar, or other methods.
  1. Water or mineral oil
    • Regular tap water can be used to fill the bubble counter so that you can see the approximate rate at which CO2 is entering the aquarium. However, the water will evaporate over time, so mineral oil can be used instead so you never have to refill the bubble counter.
  1. Electrical outlet timer
  2. Adjustable wrench with at least 1.25-inch width
  3. Scissors
  4. Spray bottle with water and a few drops of Dawn dish soap

How to Install a CO2 System

Once you have all the equipment, we recommend you follow our detailed manual and video tutorial for step-by-step instructions. To help you visualize the entire CO2 system, this high-level diagram shows how all the parts are connected:

Diagram for CO2 system


  • The regulator (B) screws onto the CO2 cylinder (A).
  • Optional manifold block add-ons can be added to the regulator (B).
  • The bubble counter (C) on the regulator is filled with liquid, and airline tubing is attached to the lid of the bubble counter.
  • The airline tubing connects to the diffuser (D), which is placed at the bottom of the aquarium.
  • The optional check valve (E) is installed in line with the airline tubing near the aquarium rim.
  • The regulator’s solenoid valve cable (F) is connected to the power adapter (G).
  • The power adapter (G) plugs into the electrical outlet timer (H), which plugs into a wall outlet or power strip.

Is it bad if the CO2 bubbles from the diffuser are reaching the water surface? No, this is normal. The key is to place your diffuser as low as possible in the aquarium. When the bubbles are released from the diffuser, they imperceptibly get smaller and smaller as they rise and the CO2 gas is being absorbed into the water.

CO2 diffuser in planted tank

Place the diffuser at the base of the aquarium to give the CO2 bubbles a longer time to dissolve into the water.

How Much CO2 to Dose

In the manual, we recommend tuning the regulator to approximately 1 bubble per second (i.e., the rate of CO2 bubbles flowing through the bubble counter) because we would rather start with a lighter amount of CO2 to keep the fish safe. That being said, CO2 dosing amounts are different for every tank, and the bubble rate is not a perfect form of measurement since each aquarium has different plant and fish stocking levels. Also, we personally do not use drop checkers to chase the “perfect” amount of 30 ppm of CO2, but instead we let nature and the plants tell us when they are happy.

When the plants photosynthesizing during the daytime, they consume carbon dioxide and produce oxygen (O2) and sugars as a byproduct. If the plants have enough light and carbon dioxide, they can produce so much oxygen that it saturates the water and you can visibly see small bubbles released from their leaves. In our warehouse, we dial the CO2 level on our plant-holding aquariums until we consistently see this “pearling” effect. Because plants are living things, it usually takes at least 24 hours after we adjust the CO2 to see any effect, so we like to wait three days before making the next change to the system.

pearling plants

Aquatic plants “pearl” or visibly produce bubbles when the water is saturated with oxygen.

When should I turn on and off the CO2 in my aquarium? As mentioned before, plants use CO2 when there is light to photosynthesize. However, the process reverses at night and becomes the respiration cycle, in which plants consume oxygen and sugars and release CO2. Therefore, we want to shut off the CO2 regulator when the aquarium light is off. For more optimized CO2 usage, program the regulator’s timer to turn on 1–2 hours before the light comes on and turn off 1 hour before the light shuts off. (If you only have one timer, you can use the same timer with a power strip so that the light and regulator turn on and off at the same time.)

Is CO2 dangerous for aquarium fish? It can be harmful for animals in large enough quantities if (1) CO2 causes the water pH to drop too quickly or (2) people try to be so efficient with the CO2 that they end up cutting off the oxygen that fish need to breathe. In the latter case, some hobbyists try to minimize surface agitation so that less gas exchange occurs and less CO2 escapes the water. However, less gas exchange also means less oxygen will enter the water, which can cause your fish to struggle and gasp for air. Our recommendation is to increase both CO2 and O2 in the water by using an air stone (or other device that agitates the water surface) in conjunction with your pressurized CO2 system. Yes, you may have to increase your bubble rate a little to compensate for the slight loss of CO2, but having enough oxygen for your fish (and plants at night) is more important and can help lead to the pearling effect that is so desired by planted tank enthusiasts.

Best of luck with your new pressurized CO2 system and we hope you have fun exploring the world of high tech plants. For more information on our CO2 regulator, check out the product page for the official manual, demo video, and more.


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