Do all aquarium plants need CO2 injection?

Do all aquarium plants need CO2? The answer to the question is a big “Yes!”. But plants do not use CO2 like animals use Oxygen. It is not the same as breathing. Plants would only need CO2 when they photosynthesize. If plants are not photosynthesizing then they do not require CO2 at all. In fact, they use oxygen when breathing. Before any conclusions are drawn though let us first understand how plants use CO2 and what they need it for. Do not worry, this article will try to refrain from getting too technical and try to be as simple as possible so it can be easily understood.

Do all aquarium plants need CO2 injection?


Photosynthesis, the process wherein plants manufacture their food would need a few key ingredients to start with. First of all, plants would need CO2 in this process. Plants do not just take up CO2 and use it directly. It is to be taken up in the leaves so the leaves can convert the carbon and water into sugars that the plants can use for energy. The excess Oxygen from this process is then released into the atmosphere or in the case of aquatic plants, into the water in the form of microbubbles. These microbubbles can accumulate on the leaves and this would be what we know as “pearling”.

Photosynthesis - plants would need CO2 in this process


The second thing the plant would need would be nutrients. Plants would need it when they are photosynthesizing for growth and general health.

Read more about methods of fertilization in this ARTICLE.


All plants require the right amount of light to start photosynthesis therefore lights are very important in the planted aquarium setup. The more light that is available, the faster the process becomes. Plants do not just turn photosynthesis on or off like turning a light switch on or off. It is started by light. Enough light will start the process for plants. If there is too much light and no sufficient CO2 or nutrients then that is where the problem begins. Plants would then start to show signs of deficiencies. These deficiencies are just plants’ way of saying that they are in fact starving to death. Deficiencies are basically signs of an unhealthy plant. An unhealthy plant does not absorb CO2 and nutrients as efficiently as a healthy one does. Without the plant’s ability to absorb these key ingredients, it becomes unhealthier. It is in fact, a vicious cycle; one that can be broken by providing the right environment for the plant and a lot of patience. All it takes is for that unhealthy plant to grow one healthy leaf and it will be on its way to a full recovery. This is how important light is to plants.

Lights are very important in the planted aquarium setup

How come some plants can survive without CO2 in the water?

Now, this is not true. Some plants can survive without CO2 supplementation or injection in the tank water but it does not mean that the water in itself does not already contain any dissolved CO2 that the plants can utilize. Tank water does contain CO2. Fish and other fauna do breathe out CO2. CO2 along with other gasses like Oxygen does get dissolved in water if the water has surface agitation. New water coming in when performing water changes does contain CO2 as well and so water changes do in fact replenish the CO2 that the plants might have consumed. CO2 will always be present in moving water. It just is not at the level that most aquascaping plants require.

Ligh-loving plants

Most aquascaping plants, especially the ones with really tiny leaves are light-loving plants. They cannot perform photosynthesis with low lighting and since they only perform photosynthesis in high light, the photosynthesis is faster and so they would need more of the CO2 to effectively do this, hence CO2 supplementation becomes a must in this instance.

The correct inquiry would be to seek out how much CO2 each type of plant would need. As a general rule, plants that can survive without strong lighting can survive without CO2 supplementation (not without CO2 at all). It will just now depend on how much light these plants receive on a daily basis.

If you'd like to learn how to set up an aquarium lighting, visit this ARTICLE.

Low-light plants

These types of plants have the ability to do photosynthesis at a much lower rate than that of light-loving plants, usually found in guides about setting up a planted tank. The Anubias is such a slow grower that it takes about 2 to 3 weeks for it to grow a single leaf. The metabolism is so slow that it would only require a very small amount of CO2 dissolved in the water for it to be healthy. There were instances that a tank full of Anubias was neglected for a month without lights turned on and when the aquarist came to check on it, the plants looked like nothing happened. They were still as healthy as the day the aquarist left them. No other plant can do this. Maybe this is the reason why Anubias is considered by most as the “king of aquatic plants''. Other plants that can survive with minimal CO2 in the water would be Java Ferns, Cryptocorynes and Bucephalandras.

Most Echinodorous species would survive without minimal CO2 as well. Even these types of plants would require CO2 supplementation when put under brighter conditions. Their metabolism becomes faster under bright lights. They have no control over it. Their growth rate becomes faster as well. Faster metabolism and faster photosynthesis equal the need for more CO2 and nutrients. For as long as enough CO2 and nutrients are provided though, faster metabolism and growth rate would mean more chances for the plant to develop healthier leaves and roots.

How do plants grow in nature without CO2 injection?

High CO2 levels in the water are not found in nature. How did these plants survive in their natural environment? Most of these plants live in flowing water. Flowing water would mean that the water around these plants is always new and so with new water comes readily available CO2 to consume. High levels of carbon are always found in nature as well, which if plants can tap as a resource would be equivalent to having high levels of CO2 in the water.

Some aquatic plants do live in stagnant bodies of water like ponds and lakes but if one observes, the ones that are found in stagnant water have a tendency to have leaves that reach to the surface as the lotus plant does. The leaves that reach the surface would then have access to CO2 found in the atmosphere. Also, stagnant bodies of water may not be moving water but there is also always a constant fresh supply of water feeding into them in the form of streams, rivers and of course, rain. It is not just to compare a planted tank with these natural ecosystems. The planted tank only depends on the weekly water change to bring in new water while these natural environments have new water coming in every second.

What about self-sustaining tanks?

Some may claim that they can balance non-CO2 supplemented planted tanks to the point wherein there is no need for water changes. That is impossible. Water evaporates and a tank without new water coming in would pretty soon dry up. They may not need to perform the regular water changes but they are performing water changes non the less in the form of water top-ups. The freshwater ecosystem be it natural or simulated will always require for new water to come in no matter how small the amount. Without new water, that ecosystem starts to die and become uninhabitable.

In general, planted tanks can be categorized into two types; the Hi-tech and the low-tech ones. The only difference is the CO2 supplementation and amount of light. Tanks that are brightly lit would need CO2 supplementation even if the plants in the tank are plants that do not require CO2 supplementation. It simply becomes a must. It can now be considered a hi-tech tank. On the other hand, tanks that are dimly lit will not require CO2 supplementation but one can only choose between a handful of plant varieties that can live in these situations. Plant variety becomes limited when choosing to go without CO2. These tanks are the ones that are considered low-tech tanks. No low-tech tank can survive with bright lights. CO2 and lighting always go side by side. An increase in lighting would require an increase in CO2 as well.

Plants that can survive without CO2 supplementation will generally be better with CO2 supplementation and brighter conditions. They develop healthier leaves and root systems. The growth rate becomes faster as well. This could not be more evident than in the case of the Dwarf Sagetareria. Dwarf Sagittaria is considered a low-tech carpeting plant. Under normal low-tech conditions, they remain very small. Leaf size would be about an inch to 2 inches in length. However, if put under brighter conditions and with CO2 supplementation leaf size can rival that of Vallisneria. They grow up to 6-10 inches and they grow twice as fast. This only goes to show that all aquatic plants no matter the classification will appreciate an abundant supply of CO2. Therefore a reliable aquarium CO2 kit is very important if you'd like to supplement CO2 effectively. Almost everything depends on the diffuser and the quality of the ceramics. The poor-quality ceramics will become clogged often and won't allow bubbles to go through it. It's good to invest in good quality diffuser which will produce a very fine mist in the aquarium, delivering CO2 to all the aquatic plants.

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Can there be too much CO2 for plants?

Light intensity matters for the photosynthesis process, the same as the amount of CO2 being injected into the tank does. But how do I know if there is just enough? The drop checker method is the best solution. The glass vessel with a CO2 reagent is placed inside the tank and as soon as the pH drops, the reagent's color will turn yellowish which means that there is too much of this gas in the aquarium. This may be very dangerous for fish therefore it's better to start with a low bubble rate and adjust it gradually.

Visit our great ARTICLE about 7 Things You Need To Know about Drop Checkers to get deeper into this topic!

If you'd like to safely inject CO2 into your aquarium plants CO2 regulator is a great tool to do this. Search for regulators with dual-stage construction which prevents end tank dump.

aquarium plants CO2 regulator

Is low-tech easier than the high-tech approach?

Newbies may start with a low-tech tank thinking it is easier to manage than a hi-tech one. In some aspects, this can be true as they have aquarium plants no CO2 equipment and in the end both solutions end up with fun. But on other aspects, low-tech tanks can be very difficult to manage, especially since problems cannot be detected until weeks later since plants in these low light conditions do not show deficiencies until much later. And correcting these deficiencies would take weeks as well.


Balancing a low-tech tank would sometimes take months. The focus in a low-tech tank should lie on how much light is allowed for the plants to survive. With hi-tech tanks, everything is much faster. Deficiencies and early signs of problems show within days and can be corrected within days too but. One fails faster with these tanks too but it is totally up to the hobbyist how to approach this hobby. With a reliable CO2 natural plant system everything is possible!

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