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Plant Care


December 13, 2018 | By Tom Sarac

by Tom Sarac

CO2 is an often misunderstood subject yet so important to grasp by anyone interested in keeping plants or fostering a naturally acidic soft water environment.

Plants are composed of 40-50% carbon (by dry weight). When one considers that the natural equilibrium of water (and the air above it) equates to a mere 6-7 ppm of carbon dioxide within an aquarium, it’s not difficult to understand why healthy plant growth rapidly strips the water of this concentration. This then becomes the limiting factor for plant growth as carbon is the key macro element they require.

While some plants are capable of getting sufficient carbon from the carbonate content in water, many species cannot. In fact, rapid growing species that are best introduced at the beginning are the ones that usually benefit most by CO2 supplementation.

Stimulating strong plant growth is also a preferred algae prevention strategy, from any perspective in a freshwater aquarium. Injecting carbon dioxide provides plants with the most easily assimilated carbon source.


During photosynthesis, light energy is converted to chemical energy within plants. The resulting chemical energy is stored as glucose (sugar). Carbon is required by the plant in using up this energy, so no matter how much light is present, you’ll always be limited by this macro element unless you supplement it properly.

Remember that plants photosynthesize when there is light available, so during the night the CO2 injection system can be shut down as there is no photosynthesis taking place.

Alternately, you can set up a small air pump and air stone on a timer to engage when your aquarium lights are switched off.


Here are a couple of methods to introduce carbon dioxide into your aquarium:

Do It Yourself:

A 2 L bottle of cola can be configured and, by adding sugar, water and yeast as the by-product, will produce carbon dioxide. One major negative to this approach is the yeast. Getting a strain that lasts a few weeks and delivers a consistent amount of CO2 is key, but what you find in a typical supermarket is not ideal. There are commercial aquatic yeast-based systems that can perform over a few weeks (like the Nutrafin units), and these are recommended for this type of fermentation system. They are safe, deliver consistent results, and will last.

Pressurized Systems:

These are more common and preferred, such as a pressurized CO2 kit and mini pressurized CO2 kit. These systems have regulators that allow you to dial in a desired dosing rate, plus you can turn them down or off at night.


The ideal concentration of dissolved carbon dioxide is 20-35 ppm. At this concentration, you can rest assured the plants will always have an adequate carbon source. Not only is growth speed enhanced with the use of CO2 injection, but the lush colours and strength of the plants is equally impressive.

It’s relatively simple to determine the concentration of CO2 present when injecting it. Consult a widely available table of values that depicts pH on one axis, and KH on the other. The values shown will be the concentrations of carbon dioxide.

Even if your carbon dioxide injection system is not providing enough to maintain as high a concentration as you’re targeting, it’s still benefiting the plants. Once you start fertilizing with CO2, be consistent in dosing level once you’ve determined the concentration you can keep.

There are more details to cover on the topic of CO2 injection, but the information above at least gives you a basic understanding on how to grow healthy and lush plants, which will inevitably improve the health of your whole aquarium in the process.


Aquatic expert Tom Sarac provides an explanation of how and why you can benefit from adding a CO2system to your planted freshwater aquarium.


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