Pressurized C02 Injection Systems
Written by Hector Ortiz   

Carbon Dioxide (C02) is a indispensible component for effective photosynthesis and plant growth.  C02 is necessary when your lighting is above the standard 2.0 watts per gallon threshold.  In lower lighting setups, supplementing C02 can only help plant growth and keep algae away.

Pressurized CO2 Systems 

At first it may be slightly intimidating, however understanding and applying C02 injection is very simple. As you will see, there are three easy, mainstream methods to inject carbon dioxide. I will walk you through the pressurized C02 setup.

Carbon Dioxide Injection Methods

1) Pressurized C02 gas

2) Do It Yourself (DIY) C02 gas,

3) Liquid C02 i.e. Seachem Excel.

What do I need for a Pressurized C02 Setup?

Pressurized C02is the best form of injecting C02 gas in a planted aquarium because it offers a continuous flow of gas that offers consistent levels of C02 .   Besides the initial setup, there’s no additional maintenance required.  Although the startup costs of  $150-200 can be deterring, the low maintenance and guarantee that C02 is constant from day to day make pressurized C02 an attractive method to be used for any planted aquarium. I will describe the main components of a pressurized C02 setup so that your aquarium is one step closer to an optimal environment for aquatic plants.

 Essential C02 Components

· Regulator

· C02  Cylinder

· Reactor/Diffuser

· Check Valves

· C02 Tubing

The Regulator

The common C02 regulators brands used in this hobby are the Milwaukee, JBJ and the Azoo C02  regulators.  These three regulators are excellent and affordable components for any system.  They can run anywhere between $75-90.  You can find them on eBay auctions, drsfostersmith.com, and a number of other online retail stores..  There are some planted tank hobbyist oriented online vendors like greenleafaquariums.com, and aquabotanic.com that are now offering their own custom build regulator systems as well.

One of the key parts to an aquarium made regulator is the a part called the solenoid.  A solenoid is essentially the on/off switch to your regulator.  When on, the solenoid opens a magnetic gate that allows gas to flow from the cylinder to the tubing line. When turned off, C02 flow stops. When you place a solenoid on a light timer, you can automate your C02 system and have C02 flow stop when the lights go out, and have the flow resume when the lights go on. That’s important because plants utilize (photosynthesize) carbon dioxide when the light goes on.

Aquarium regulators will have another necessary component called the needle valve.  This  allows you to change the rate of gas flow. C02 gas is measured in parts per millions (ppms) or observationally by the amount of bubbles flowing into a tank per second.  A bubble counter (a see-through container filled with water) allows the aquarist to see and count the bubble rate. Generally, depending on your tank size,  a rate of 3-5 bubbles per second is a good rate to have for a planted aquarium. This will produce around the optimal 30 ppms of dissolved C02 gas in a planted aquarium.  A CO2 drop checker product can also help measure your CO2 levels.

5-10 lb C02 Cylinder

C02 cylinders are best bought locally from your fire extinguisher supply depots and welding supply shops.  Pick up the phone book and call around.  With the paintball hobby in full swing, these C02  distributors won’t blink an eye when you say you need a  5-10 lb C02 cylinder for your aquarium. 

A 5 lb cylinder can produce at least six months of C02 for your aquarium. The bigger, 10 lb cylinder can last double that. I recommend getting the largest sized cylinder that can fit in your home and under your aquarium The cylinders can run anywhere between $60-100  from  a local supplier. Refills are about $20 at most locations.

In the heyday of introducing pressurized C02 in the late 1990s, hobbyists used to make a big stink over whether or not one should get an aluminum cylinder or a steel-composed cylinder. In all honesty, it doesn’t make a squat of difference when it comes to planted aquariums.  A full steel 10lb  C02 cylinder weights around 40 lbs. Aluminum cylinders are lighter so I suppose you should take that in mind if lifting 40 or so pounds is difficult. Aluminum cylinders can run about $50 more than a steel cylinder of the same size.

It is also important to remember your  C02 cylinder will be hidden under your aquarium and out of sight. So when your

C02 distributor tells you they only have refurbished cylinders for sell, don’t worry and just get it.  C02 cylinders are tested about every 5 years by the distributors to ensure they are safe enough to hold C02 under pressure. You’ll find C02 cylinders dating back to the 1960s still on the selling floor today. So the worn looking refurbish cylinder will work just as well as a new shiny one.

Reactor/Diffuser

In my opinion, reactors and diffusers represent the most difficult aspect of the system.  There are many ways to dissolve the C02 gas. The common methods include:

External Reactor

An external reactor such as a Aquamedic 1000 or a DIY reactor is set inline with the plumbing of your canister filter. It works by dissolving C02 gas in the turbulent water created inside the external reactor. This is an effective way of dissolving C02 without worrying about cleaning out an in-tank diffuser  like the ones describes later.

Remember to put the external reactor on the water output side of your canister filter to ensure that only clean water goes through it.

There are many tutorials available on the internet on how to make your own DIY External reactor so at the moment I will not go into the process. The key for any external reactor is to get as close to 100% dissolution of your C02 gas before it enters the aquarium.

C02 Glass Diffusers

Using a glass diffuser or “pollen glass diffuser” as it can be referred to after an Aqua Design Amano product, is another effective means of introducing carbon dioxide to a tank. This diffuser is a glorified (yet efficient) airstone that is placed inside the aquarium underneath a flow of water.

What makes it so effective? The diffuser disc is composed of tiny pores that results in very fine, mist like bubbles as the C02 bust through the membrane.  The resulting fine bubbles are easily dissolved into the water column, and some of the mist-like bubbles even find their way underneath plant leaves which is said to aid in aquatic plant C02 absorption.

Glass diffusers in the past three years have taken the hobby by storm. Most planted aquarists now use this method over external reactors. The caveat of using glass diffusers as I  mentioned earlier is that they require frequent (every 2 weeks) cleanings to keep the disc surface as clean and effective as possible.

Over time, algae and bacterial film may grow on the disc surface which covers up the fine pores on the surface. This results in larger, and less dissolvable bubbles of C02 gas. The remedy to a dirty disc is to soak the glass diffuser in a solution of bleach for ten minutes during a tank cleaning.  Some people purchase two diffusers and swap the dirty one out for a new one to save time.

C02 line in the intake MethodCO2 Glass Diffuser

Now this is the “cost efficient” way of dissolving C02. It’s as simple as sticking the output end of the C02 tubing directly into a filter intake and using your filter as a reaction chamber to dissolve the gas. Sounds easy enough? Well it is, but filters aren’t exactly made to handle the acid byproduct that C02 gas inherently has. Some filters parts such as the impeller, rubber areas, and motor may wear out prematurely as a result. In extreme cases, a filter may stop working altogether if the gas builds up in the filter and stops the impeller from catching water. 

However, this method can be effective depending on how well the C02 dissolves as it makes it way through the filter.  Just be careful.

The dissolution method that works best will vary with every tank. I personally like to use external reactors because I like to take one less thing out of the tank maintenance process. But I know several others swear by the extra effectiveness of bubbles from the glass diffusers. As long as you’re pumping C02 gas into your aquarium, I’ll be happy and your plants will be happy too.

Check ValvesBrass Check Valves

Check valves are designed to prevent water from back siphoning out from the tank when the C02  flow is turned off or runs out.  The best check valves are the metal type (brass) check valves.  Plastic check valves will work but they are susceptible to C02 deterioration and will need yearly replacing. These are placed on the C02 tubing between the regulator and  diffuser end.

You might think that you won’t need a C02 check valve, but you’ll soon realize your mistake. Water will siphon back out from your aquarium and down to your expensive C02 regulator. Getting water inside the regulator or more likely the solenoid part will render your expensive gismo inoperable.

C02  Tubing

Typical airline tubing and silicone tubing are highly permeable to C02 gas and they  can become brittle/crack over time.  Specialized C02 tubing like Poly urethane tubing is one of the best choices for offering low gas  permeability and C02 resistant degradation.  To  ensure 100% of the C02 gas makes it to the tank use tubing that is made for C02 gas.

pH Controller

This is an optional component for a pressurized system. A pH Controller such as the Milwaukee SMS125 pH Controller helps regulate the amount of C02 injected in a tank.  The user sets the pH level at a desired level, and the controller will make sure it stays around that level (much like a heater thermostat).  The reason why this is an optional product is because a light timer designed to turn off the solenoid at night will do the same thing.  A timer will eliminate the flow of C02 when the plants are not using it if it is set to turn off when the lights go out. off.

What do I need for  DIY C02?

DIY C02 is an applicable system for 30 gallon tanks or less. It uses yeast, sugar and water to produce a reaction that has C02 gas as a byproduct.  The reaction can last anywhere between 2-4 weeks and will need to be replaced regularly.  Compared to Pressurized C02, it is economically cheaper, but the time and maintenance required to  keep it producing gas at the highest level can be costly. I will talk about how to make a DIY C02  setup in a future article.

Can I use Seachem Excel for C02?

Seachem Excel is an organic based liquid carbon source.  It requires daily administration but is very effective at providing C02  to plants.  Seachem Excel can be used alone or as a supplement to DIY C02 or pressurized C02. In the long run Seachem Excel can become expensive to use every day on a large tank, but on tanks under 20-30 gallons it is relatively inexpensive.  To minimize costs buy Excel in bulk 2 liter bottles for around $23.

Pressurized C02 Wrap-up

Now that you know all about pressurized C02 and have been introduced to the other common methods of C02 injection, be sure to inject the gas slowly if this is your first time. Also, be sure to secure your C02 cylinder inside your stand and away from any wandering kids who may be interested in turning knobs or have a tendency of tipping things over. Once you begin introducing C02 you’ll notice within a few days the positive effects it has on plant growth and health. You’ll wonder to yourself, why you hadn’t started with pressurized C02 in the first place.