Do planted tanks require CO2?


Although all plants require carbon dioxide to grow, some aquarium plants require more CO2 than others to thrive. These high-demand aquatic plants typically originate from areas naturally rich with carbon dioxides, such as rivers and streams. When placed in an aquarium, these species require additional CO2 supplementation to meet their needs. This article highlights some more demanding plants (red plants usually) used by many aquarists to create amazing displays throughout the aquascaping hobby.

planted aquarium

What you need to get started with CO2 injection

Before delving into the plant species, let's remind ourselves of the essential equipment for providing aquatic plants with CO2. At a minimum, you'll need a CO2 bottle and regulator, an appropriate diffuser or reactor, a bubble counter, a drop checker and a solenoid valve. On our website, you can find everything needed to get started (minus the CO2 cylinder) here.
When a planted aquarium receives CO2 injection, we refer to this as a high-tech tank. CO2 injection should be paired with high-powered lighting and regular fertiliser dosing. All of this combined will supercharge the photosynthesis process needed for healthy plant growth, resulting in increased growth rate, brighter colors and healthier plants for us to enjoy.

How do plants use CO2 to grow?

Lets us briefly explain a process called Photosynthesis. During this process, plants utilize the energy from light to turn carbon dioxide (CO2) and water (H2O) into oxygen (O2) and carbohydrates like glucose. This is a crucial process for all plant growth since it forms the basis of organic compounds necessary for plant health. While photosynthesis requires lots of light, it also relies on CO2. Without an adequate supply of CO2, plants cannot carry out the process correctly. This can stunt the growth of your aquarium’s aquatic plants and prevent them from reaching their full potential.

aquarium plants

Do you need CO2 for a planted tank?

If you have never added carbon dioxide to your aquarium water, or perhaps you have always avoided high lighting in your planted tanks, you may ask yourself, do I need co2 for planted tank success? The simple answer is yes. CO2 is vital to the photosynthesis process that occurs in aquatic plants. Without the correct levels of CO2, the plant will not be able to perform its energy conversion from light energy (sunlight) into oxygen and carbohydrates, thus stunting its growth. Therefore, it is essential to consider adding carbon dioxide supplementation if you want your planted aquarium.
It is proven that ALL aquatic plants do better when provided with co2 in your aquarium. It is simply a matter of balance. If you have very low light, then it is not necessarily necessary to inject CO2. However, if you have medium–high lighting and regular fertiliser dosing, injecting CO2 in your aquarium for optimal growth is highly recommended. So, in short, the more factors you give your plants to grow optimally, the better.

So, what aquarium plants need CO2 injection?

Aquarium plants' CO2 requirements vary from species to species. Generally, fast-growing stem plants benefit most from CO2 in planted aquariums. This includes stem plants like Hygrophila, Vallisneria and Ludwigia, carpeting plants such as Dwarf Baby Tears (Hemianthus callitrichoides), and most medium to large background aquatic plants such as Amazon Swords (Echinodorus). Other beneficial plants include Java Ferns, Anubias and Cryptocorynes.

Before selecting the plants you wish to use in your next planted aquarium, please research the individual plants and their CO2 requirements. This will help ensure you have a successfully planted aquarium setup. If you inject CO2, follow the plant care instructions as closely as possible for optimal results.

Many plants will produce completely different results with and without additional CO2 injection. With CO2 added, the plants will generally be larger, more vibrant in color, and grow faster than they would without it. When living in an aquarium environment where additional CO2 is present, plants will grow much larger than their original size when grown in soil or other mediums.

Leaves can change from green to red when receiving CO2 combined with bright light and can have a much more full appearance. In some cases, even plants considered slow growers in soil or other mediums may thrive much faster with the additional CO2 injection.

  • Rotala rotundifolia
  • Rotala sp. "colorata"
  • Cryptocoryne wendtii 'Flamingo'
  • Alternanthera reineckii 'Mini'

The above plants do very well to maintain beautiful red, pink or orange leaves when receiving CO2 injection. Of course, correct water parameters are still essential to keep in mind when trying to maintain an optimal aquatic experience.

How do I know if my aquarium plants need CO2?

As mentioned above, most aquarium plant producers provide care information for their products. Additionally, looking at the plant's leaves is an easy way to tell if additional CO2 is needed for optimal growth. If you notice your aquatic plants start to become less vibrant, lose color or are not growing as quickly, adding CO2 may help them thrive. Monitor your tank, and don’t forget water changes and regular maintenance to keep your plants looking their best. With proper care and maintenance, your aquatic plants should thrive with the extra nutrients provided when we add carbon dioxide to our planted tanks.

What about floating plants?

Floating plants are unique because they do not require CO2 injections to survive. Because they are suspended in the water and receive plenty of light, floating plants require very little outside nutrients to maintain optimal health. However, if you decide to use a CO2 injection system for your floating plants, monitor your tank chemistry levels frequently. Too much or too little CO2 can be detrimental to your aquatic plants. Additionally, maintain your tank and regularly perform water changes as needed. With the proper care, your floating plants should thrive with or without additional CO2 injections.

I prefer a low-light aquarium. Can I still add Carbon Dioxide?

If you have a low-light setp, you can still add Carbon Dioxide and benefit from faster growth. As long as you monitor the levels of CO2 carefully and adjust if necessary, you can maintain healthy plants. Be aware that your existing lighting may not be adequate to maintain higher levels of CO2 in the water column. However, with careful monitoring, you should still be able to have healthy aquatic plants or even add some other plants that you may not have been able to attempt before you added carbon dioxide.
Low-light aquariums and even moderate lighting setups often go hand in hand with biotope ecosystems, and you may find that many of the plant species found in the natural location of these fish species may include some plants that receive high levels of carbon dioxide so to add carbon dioxide would mean access to many more plant species than before.

Blackwater aquariums

This low-lighting tank replicates the naturally found dark brown rivers and streams by adding dried leaf litter or seed casings, often called botanicals. Adding carbon dioxide to an aquarium also works very well with blackwater systems, as it will help provide a balanced environment to the tank. Plants in a blackwater aquarium tend to do well in low-light settings. Stem plant species are prevalent in such setups, while carpet plants would not typically be found in a blackwater setup because they require much more light than is possible.
When we add carbon dioxide to blackwater aquarium water, we should take extra care and monitor the pH level closely. While the use of a drop checker provides enough indication in a high-lighting or even a moderate-lighting aquarium, a blackwater aquarium may make it difficult to view the solution accurately.
The nature of these setups creates a naturally low pH environment, with a target range of 6.5-7.0 being ideal for most blackwater aquariums. With this in mind, adding carbon dioxide can cause an imbalance in pH levels if not monitored appropriately. To combat this, it is essential to use a pH controller or monitor the pH levels regularly and adjust CO2 injection as needed. The standard use of a drop checker (even in a moderate lighting blackwater aquarium) should not be entirely depended on alone.

The proof that CO2 works in your aquarium

So you have researched your plant care requirements and decided against unwanted algae growth and now run a CO2 system in your aquarium. How do you know it is working effectively? The most reliable and accurate way to measure the CO2 content of your aquarium is by testing with a drop checker. This is done by adding drops of special reagent solution into the bubble counter. The color change indicates the CO2 level within the water, with green indicating that there is a sufficient amount for plant growth. Other methods for measuring CO2 include pH and KH measurements. However, these do not directly measure the amount of CO2 but instead, indicate if there is a change in CO2 levels.

planted aquariums


When it comes down to the question of which plants require carbon dioxide to survive underwater. If we genuinely want the best environment for our plants and want them to survive and thrive, we should consider injecting pressurised carbon dioxide into any planted aquarium.