CO2 for Aquariums - Setting Up - Planted Tank Mates

CO2 for Aquariums – Setting Up


Takashi Amano changed the hobby when he introduced CO2 for aquariums.  He wanted to mimic his underwater photography by recreating the natural scenes in a planted tank.  His vision and ingenuity made the industry what it is today.  You’ll often hear CO2 systems associated with the term high-tech setup.  This generally includes the combination of intense lighting and a CO2 injected system to aid plants in photosynthesis.  Low-tech setups do not utilize CO2.

CO2 in Nature

In nature, plants take in CO2 and expel oxygen.  Mammals breathe in oxygen and exhale CO2.  It’s a cyclical and co-dependent process.  For plants to process CO2, they need natural sunlight and water. You heard this word in grade school and you hear it all the time in planted tank forums: photosynthesis.  

When under water, the requirements are the same.  Ponds, lakes and rivers have the advantage of natural movement, surface agitation and gas exchange.  Your aquarium is a contained ecosystem that is completely limited by what you put in and how the elements interact.    Trying to mimic this system can be difficult, but that’s where introducing CO2 can help.  

Diagram showing process of photosynthesis and cellular respiration
CO2 in a Planted Tank

CO2 is a supplementation for submerged aquarium plants.  It definitely helps plants grow fast and at higher concentration can keep algae under control.  There are many aquarium plants that can thrive in a tank without CO2, yet at the same time, many aquarium plants that require it. Liquid carbon is a common alternative to CO2 injection.  Though not as efficient and effective, many aquarists will use this for low tech setups.  Be careful though when using liquid carbon or CO2, because high levels can be harmful to all livestock.

CO2 Equipment Breakdown

CO2 Tank

There are a handful of things you need to set up your CO2 system.  It may seem a bit overwhelming at first, but it’s a relatively simple setup.  The first thing you need is a CO2 tank.  Avoid using a paintball canister.  The regulator requires the paintball canister to be placed on its side and that’s not good for long term use.  Best is to get a simple 5 lb tank that would generally last months.  You can easily find the tanks on Amazon.  To fill up, check out paintball shops, beer supply vendors or any gas supply store.  A 2.5 lb tank is an option for smaller tanks, but check with your gas supply store as some places cannot refill anything smaller than 5 lbs.

CO2 Tank with Generic Regulator – 2.5 lb & 5 lb tank – available on Amazon
CO2 Regulator

The next item required is a CO2 regulator.  If you open your tank valve without a regulator, gas will blast out and deplete the tank in minutes.  A regulator controls the pressure and amount of gas coming out.  For the planted tank hobby, most will get a CO2 regulator with a solenoid.  The solenoid is an electronic device that allows the regulator to be plug into a timer. With the solenoid, you can program your CO2 to turn on and off automatically at specific times.  If you’re using a Co2 regulator without a solenoid, you have to manually turn CO2 on and off daily.  This can quickly become a problem with consistency, so it’s worth the extra cost for a regulator with solenoid. 

CO2 Regulator with Solenoid – available on Amazon
Bubble Counter

Following the regulator is a bubble counter.  A bubble counter will help you gauge how much CO2 is being released into your tank.  It has a chamber you fill with water (sometimes oil) and you count how many bubbles per second to calibrate your tank. There are a few options when it comes to bubble counters.  Some are attach to the regulator and there are bubble counters that connect to the airline tubing. Tube options can range from a plastic chamber to a nice piece of glass.

Glass Bubble Counter – available on Amazon


CO2 Regulator, Bubble Counter & Solenoid – available on Amazon
CO2 Diffuser

Once you have the bubble counter set up, you need to release CO2 into your tank. The most common method of CO2 injection is placing a diffuser inside your aquarium. This is commonly a steel or glass looking device, somewhat shaped like a traditional smoking pipe. It typically has a ceramic disc that helps break down the CO2 gas into tiny micro bubbles, making it easy for your water to absorb. You could also release CO2 via an In-line system.  In-line systems typically require a canister filter where you can attach an atomizer or reactor to the outflow tubing.  These devices saturate the CO2 before it outflows into your tank.  Atomizers and reactors are popular for minimalists who want to avoid having a diffuser inside the tank.  You can read more about those 2 options here.

CO2 Diffuser – available on Amazon
CO2 Drop Checker

Last but not least, you’ll need a drop checker.  This is an independent device that’s placed inside your tank and is not connected to your CO2 setup.  The most popular is a glass dropper where you place a solution inside that changes color.  Bright green means you have a good amount of CO2 saturated in your tank.  This is optimal during the day when your lights are turned on.  When CO2 and lights are turned off, the drop checker gradually turns blue.  This generally occurs in the late evening and early morning.  Yellow indicates too much saturated CO2 and you should do a water change if livestock is showing signs of stress.

Drop checker – available on Amazon
Monitoring CO2 levels
Airline Tubing and Check Valve (backflow preventer)

Airline tubing connect all the equipment noted above.  Be sure to get CO2 tubing that’s made of harder plastic, not your standard soft silicone. Silicone tubing can become porous overtime and leak, so you’ll want the more rigid tubing that can handle the pressure. Also, don’t forget the check valve. It’s a simple device that prevents water from siphoning back into your system.

Black CO2 tubing – available on Amazon


Check valve – Amazon


You may have read a lot about DIY CO2 systems.  They’re definitely out there and there’s even blogs documenting a DIY system at a fraction of the cost.  Most utilize solutions of yeast, baking soda, vinegar, citric acid; all simple household items.  While a DIY system will definitely save money, it’s very challenging to keep stable and consistent.  The pressure and intensity can deplete.  External conditions like temperature can impact the consistency.  Plus, can you imagine setting up your DIY solution everyday before rushing out to work?  The initial cost savings may quickly be outweighed by the inconvenience, mess and fluctuating quality being delivered to your aquarium.  It’s worth a try if you’re into DIY, but it will impact the quality of your planted tank unless you maintain a consistent routine.

DIY CO2 System
DIY CO2 setup

All Things Considered

You can absolutely keep a successful planted tank without CO2.  However, providing CO2 will expedite the growing process and give you more options for your planted tank.  Its initial cost can be high, but maintenance cost and performance is relatively low.  When you automate a system, it’s consistent, stable, and can deliver CO2 safely to your aquarium.  Too much CO2 is not ok, so monitor levels and prevent it from suffocating livestock.  There’s also no such thing as a one time setup.  If your plants are growing too fast, scale down the CO2.  When algae starts to bloom, dial it up a notch.  If livestock are inactive and flapping their mouth, CO2 might be too high.  Generally check your water parameters and take notes before making adjustments.  See below for some CO2 setup diagrams.

CO2 Setup Diagrams

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