Role of CO2 in the planted aquariums

Sometimes an aquarium is not just about fish but also the plants that reside inside it. Hobbyists always look forward to attractive fish as well as aquatic plants that can bring life to their aquarium. It is no surprise that a planted aquarium is more alluring, natural in appearance and brings enthrallment to the fish too.

Other than these the biological roles that aquarium plants play are:

  • Supply oxygen to the organisms inside the tank
  • Aids in decontaminating the water
  • Offer hiding and playing places to the aquarium creatures

Aquatic plants are no exception when it comes to getting specific doses of essential components for healthy living. Therefore, it is important that they remain equipped with every essentiality that makes the survival of the plants easy.

Some of the major requirements of most of the aquarium plants are

  • Right substrate
  • Perfect lighting
  • Ideal dose of Carbon dioxide
  • Essential micronutrients

In this article, we will discuss the role of carbon dioxide and how its absence may affect the survival of aquarium plants.

Some amount of carbon dioxide is already present in the tank as a byproduct of fish respiration and some from contact with the atmosphere. However, this amount is not sufficient for the plants to fulfill their demand for this important element. Therefore adding extra carbon dioxide for a flourishing aquarium is a must.

When carbon dioxide becomes essential

The carbon dioxide absorbed in the water from air is just a few ppm (parts per million) which is not sufficient for the plants. If in case this amount in ppm increases, the air contact will shed the excess CO2 naturally. Moreover, if the surface is agitated vigorously, this essential gas will again shed in the air.

Whether supplying extra CO2 is important or not depends upon a variety of factors. It is not essential that everyone who has an aquarium give additional supply to the tank. The major factor which determines its need is lightning in your tank.

If the plants require low and moderate lighting and you have provided so in the tank, the need to supplement extra CO2 ceases.  However, if the lighting is excess, the growth of algae may bloom inside the aquarium. This is when the need to supply carbon dioxide becomes necessary to seize their excessive growth.

The criteria which determine the lighting are as below:

  • If the tank is supplied with around 1 ½ watt per gallon which is also the minimum in regards to lighting it is considered as low lighting in the planted aquarium.
  • When the tank has 2 watts per gallon of lighting, it falls under moderate lighting for a planted aquarium.
  • If there are 3 watts per gallon or more light, it comes under high lighting condition where supplying extra carbon dioxide becomes a must.

How extra carbon dioxide affects the planted aquarium

Supplemental carbon dioxide endows immense benefits to the health of the plant. Once supplemented, you may experience your plants becoming robust and healthy. Plants with a slow growth rate will resume their normal growth pattern, and you will see them thriving all over again. The plants that have become fragile will grow thicker and better. This wonderful positive effect of carbon dioxide varies from plants to plants and their individual requirements. Some plants can be seen getting benefitted more than the others.

The filtration system of the aquarium also influences the supplementation of carbon dioxide to the plants. If the rate of water flow is high, there will be more aeration which directly implies to the fact that more gas exchange will occur at the surface of the water. Therefore, if you put efforts in reducing this flow, the chances of carbon dioxide loss will subside as well.

Adding carbon dioxide to the tank

If after proper research and judgment you have decided to supplement carbon dioxide to your tank, you may take different routes to do so.

  1. Get a diffuser: Ceramic or glass diffusers work wonders in supplementing carbon dioxide to the tank. There is a porous ceramic disc with a glass fixture connected to carbon dioxide line. The gas is infused inside the tank as you open the line and device develops the desired pressure.
  2. Yeast-based diffusion: In this way, the carbon dioxide is produced as a byproduct of fermentation. Although it is inexpensive to set up and run, the drawback is you get uncontrollable supply which is generally inconsistent as well.
  3. Through aerosols: The control over diffusion is less with this method, and they go well only with small tanks. However, you have to refill it regularly to fulfill your requirements.
  4. Using liquid carbon fertilizers: You may find this product from a number of brands. The active ingredients in almost all of them are same with the same instructions to use. The only thing that differs is the concentration of carbon dioxide.

How much carbon dioxide for your tank

Once you have decided to supplement CO2 and the way to induce it, next step is to know how much carbon dioxide is needed for your tank. For this, you have to know the pH of the water and the carbonate hardness of your aquarium. You may get the values by having a water test kit.

It is advised that a planted tank should have CO2 between 20 to 25 ppm. If the value rises above 30 ppm, not just the fish will come under stress but the plants as well. It has been seen fish dying when the CO2 levels go to 50 ppm and above. Therefore you should be cautious in supplying the right amount so that plants and fish both can thrive well.


A well-planted aquarium with lush greenery grabs the eye of the viewers instantly. However, it is essential that you learn the basics as for how to maintain the plants as well as fish without any stress.  Therefore, creating an ideal environment is important.

Believe me, nothing is possible without plants, and once you have a planted aquarium, you will know about it.  So get some beautiful plants for your aquarium now and make it eye-catching.

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