A Complete Pressurized CO2 Guide


Hi FishLore,

This guide will go through all components of a pressurized CO2 system and which components are actually necessary to make a successful pressurized CO2 system. I will also include information on how to use the CO2 system and suggestions as to which products to buy.

Components of a Pressurized CO2 System:
1. CO2 Tank/Canister
- These CO2 canisters are the source of CO2 for your system and hold liquid, compressed CO2 within them. These tanks must be handled with caution and should be kept out of direct sunlight. Always keep them upright and make sure that your tanks are certified for CO2 use.
2. CO2 Regulator (Essential) - This is the heart of your system that is responsible for regulating how much CO2 enters the water stream. It is advisable NOT to skimp on the quality of your regulators because a faulty regulator can easily gas your fish. CO2 regulators sold for planted tanks are often a single stage or dual stage.

Single stage regulators are cheaper, but they are prone to end of tank dumps. An "end of tank dump" occurs when the amount of pressure within the CO2 tank reduces to the point where the regulator cannot effectively regulate the amount of CO2 entering the water. This causes a bunch of CO2 to be dumped into your aquarium at once, which often kills the fish.

A dual stage regulator will often be more expensive, but is well worth the expense as it will prevent an end of tank dump because it is essentially two regulators in one body. The delivery pressure will always be held consistent, adding safety to the system and reliability/consistency in the bubble count even as the pressure in your CO2 tank drops over time. NOTE: A dual stage regulator is not the same as a dual gauge regulator. A dual gauge regulator just refers to the two circular pressure gauges on the regulator. One gauge will report the amount of CO2 inside the CO2 tank, and the second gauge will report the amount of working pressure within the regulator.

Try to purchase a CO2 regulator with a solenoid valve. This allows your CO2 to be turned on and off using a timer, which automates the process of CO2 and prevents user error in operating your CO2 system.

CO2 regulators have a bubble counter and a needle valve, which allows the user to adjust the amount of CO2 entering the water.
3. CO2 Tubing (Essential) - CO2 tubing looks similar to airline tubing, but is stiffer and better quality. It prevents CO2 leakage in the line and lasts for a long time. It is much better to use CO2 tubing than silicone tubing because it will be more reliable over time. The CO2 tubing connects to the regulator and is needed to transport the CO2 from the regulator to the aquarium.
4. CO2 Diffuser (Essential) - CO2 diffusers are items that allow for CO2 to be dissolved within the water column. Large CO2 bubbles will not effectively dissolve within the water column, hence a diffusion mechanism is needed. There are a few common types of CO2 diffusion items, each with their own pros and cons. I will list the most common ones.
  • Ceramic Diffusers/Atomizers - These are by far the most common and are effectively an airstone - but for CO2. CO2 is forced through a ceramic disc which creates small microbubbles. These are good for tanks under 40 gallons. CO2 atomizers are just like ceramic diffusers, except they create even finer microbubbles. It creates a CO2 mist within the water which is even more effective for diffusion into the water. When comparing ceramic diffusers to atomizers, an atomizer is almost always a better choice. The problem with both products is that they get dirty over time and will need to be cleaned periodically with a bleach solution. Additionally, it is easy for plants to block the diffusion of CO2 from such a small source so extra diligence is required to make sure that the diffusers are not blocked by the hardscape or plants. Finally, this the least efficient method of CO2 diffusion. For smaller tanks, the amount of CO2 lost is negligible, but for larger tanks, using so much CO2 will start to add up over time.
  • CO2 Inline Diffuser - These devices can be used in a canister filter's outflow, which injects CO2 through an even finer ceramic disc. Combined with the water flow coming out, it is a highly efficient way to diffuse CO2. It's great for tanks that are 20 gallons and up. It can saturate large tanks if utilized correctly. High amounts of volume can be pumped through these diffusers which makes it good for even the most powerful of filters. They also do not need to be cleaned often. The major con with this product though, is that they create a fine mist within the water, creating a "sprite" effect. The entire tank will be saturated with CO2 microbubbles and will appear as if the tank water is actually sprite. This can be extremely irritating for some people as it can ruin the aesthetic, but it's a great device for using CO2 effectively and efficiently for larger tanks. Additionally, as the flow of your canister filter becomes impeded over time, the CO2 will start to become negatively impacted so regular filter maintenance is necessary.
  • CO2 Reactor - These devices can be used with a pump or canister filter in order to achieve 100% CO2 diffusion into the water column, making it the most efficient device around. It doesn't need to be cleaned often and doesn't create a sprite effect either. It would be best to use CO2 reactors on larger tanks. The only true drawback to this device is that it doesn't create mist. Although CO2 mist could be aesthetically unappealing to some, photosynthesis can be increased as CO2 mist attaches to the leaves. If the CO2 is completely dissolved in the water column, it is not as effective for plant growth.
  • From Left to Right (Ceramic disc, atomizer, inline diffuser, reactor)
5. CO2 Drop Checker (Non-essential) - These devices use a 4dKH solution to approximate the CO2 concentration within the water. A blue color indicates a lack of CO2, green indicates approximately 30ppm, and yellow indicates too much CO2. It should be known that CO2 drop checkers are not accurate. I often see these being used as the "end all be all" of CO2 concentration within the water. They take hours to react to changes of CO2 within the water column and even then, it is difficult to correlate an exact color to an exact concentration. I've used drop checkers in the past but have since stopped using them because they are so inaccurate. In my opinion, this device can be skipped altogether and is not essential to use.
6. Teflon Tape and CO2 Washers (Essential) - Teflon tape should be used around the area where the regulator screws on. Teflon tape meant for gas is ideal to use. CO2 washers are commonly utilized, but are only necessary for regulators that actually call for it in their use. Do not use CO2 washers if the regulator does not need it. CO2 washers are meant to be used 1 time and are put between the area where the regulator attaches onto the gas tank.

7. Soapy Water Dropper (Essential) - Find some sort of dropper bottle and fill it up with a soapy water solution. When your system is entirely assembled, this soapy water solution should be squirted onto all connections in order to identify gas leaks. This is a mandatory step because even the smallest leaks can cause a major loss or malfunction in your CO2 system.

How to Use Pressurized CO2 Systems:
Now that you have all the necessary components and your system is assembled, it is necessary to know the proper methods in operation your CO2 system.

First, your CO2 should be placed on a timer. The CO2 should turn on one hour before the lights turn on, and turn off one hour before the lights turn off. This will allow the CO2 to build up to a good concentration before your plants start photosynthesizing.

Your CO2 diffuser should be placed in an area of the tank in which the flow of water will be able to effectively disperse it around. For ceramic discs and atomizers, the following picture by Dennis Wong is a helpful guide of placement:

The X in the picture marks the area where the diffuser should go. In this way, the outflow's down current will carry the CO2 throughout the tank while keeping it in the water the longest. This circular pattern of water movement should be implemented with CO2 diffusion, no matter the device used, in order to encourage could gaseous exchange and proper circulation.

If using a CO2 reactor or inline diffuser, make sure that the outflow in which the CO2 rich water leaves is directly in a manner that will effectively circulate the entire tank while not gassing off the CO2 immediately. For instance, don't aim the outflow at the surface, but instead direct the outflow downward so that the CO2 will stay in the water longer.

In order to know how much CO2 to inject within the water, it is necessary to be highly observant of your plants and fish. Disregard your drop checker or your pH/kH tests and just watch your livestock. Bump the CO2 high enough until the point that your fish become slightly stressed and start to gasp at the surface for air. Then lower it just a tad down. Lower it just slightly so that the fish return to their normal state, but the CO2 levels aren't lowered significantly. This threshold CO2 level between stress and no stress is where you want the CO2 level to be at permanently. This level is the perfect concentration of around 30-45ppm CO2 which is ideal for aquatic plant growth. Please note that this is a SLOW process. Adjustments to the needle valve should be made every 30 minutes. Do not rush this process. It will likely take many hours to get the initial injection rate correct. Over the coming weeks as your scape grows in, you might need to keep adjusting as plant mass increases and CO2 demands consequently rise too.
It is also important to note that for tanks with shrimp, their CO2 tolerance is much lower and this must be taken into account when calibrating your CO2 injection levels.

As your scape grows in, make sure you keep up with maintenance. It is vital that the CO2 diffusion methods are not hindered by overgrowth or a lack of cleaning. Check the pressure gauges on the regulator regularly to monitor the amount of CO2 you have left in your CO2 tank.

Products I Recommend From Personal Use
I've been using CO2 for a couple of years now and there are few products that have lasted the test of time and the elements, as some of my CO2 system are outdoors. I am not sponsored by these companies and am simply giving a trustworthy/reliable source to buy from.

For regulators, I highly recommend CO2Art regulators from co2art.com . I personally use the base model or the PRO-SE. It is a dual stage regulator made in Germany, and has a stable bubble count, easy to read gauges, and just high quality materials overall. This regulator is by far my favorite one that I've used and it is very affordable for a dual stage regulator. Most other high quality dual stage regulators cost upward of $200, but CO2 art is very affordable with their base model coming in at $150.

For CO2 tanks, I recommend refurbished CO2 tanks from beveragelements.com . CO2 tanks are so expensive, but this company makes refurbished CO2 tanks that are relatively inexpensive. The tanks are high quality and have lasted for years outdoors. For my customers, I recommend their 7lb tanks and for people with larger tanks like myself, I recommend their 15lb tanks.

For all types of CO2 diffusers, CO2art and NilocG are both highly reputable companies with great products. I personally have a NilocG inline diffuser that works great. Many of my customers have used various CO2art and NilocG diffusers with great success and my customers have had no issues with the products either.

Please do not skimp on CO2 products to lower the price. It is important the items used are good quality because CO2 has the potential to be dangerous to your livestock if used incorrectly. Additionally, pressurized gas in itself can be dangerous if used incorrectly, hence only trustworthy equipment should be used.

Thank you for reading, please feel free to ask any questions you may have.


This is a really awesome guide, thanks Vishaquatics.
  • Thread Starter


To address a question I am seeing a lot:

"Do we need to run an airstone while CO2 is being injected?"

The answer is a definitive no. The airstone adds too much surface agitation and other gas to the water where it would essentially gas off most of the CO2 that you are injecting into the water. It would be like trying to fill up a bath tub, only to have the drain wide open. Very little water would fill up the tub, and the drain would be wasting all of that water.

If you do want to run an airstone, it can be run at night when the lights and the CO2 are off. This will help to gas off the CO2 in the water since the plants won't use it at night. It is not essential, but some people like to do this.

Surface agitation is an important component of CO2 injection. It helps to make sure that oxygen is entering the water, which is vital for both plant growth and the health of the livestock. However, too much surface agitation will waste CO2. Good surface agitation will occur if you...

1) Use a surface skimmer

2) Have a hang on back filter which gives a light ripple to the surface

3) Have some sort of canister filter outflow or powerhead aimed at the surface which creates a light ripple.

A light ripple across the surface is all that is needed. Too much turbulence is not necessary.
Top Bottom