do aquarium plants need co2?

Setting up a lush, vibrant planted aquarium is a dream for many aquarists. The sight of healthy, thriving aquatic plants swaying gently in the water is not only visually appealing but also beneficial for the overall well-being of your aquarium’s ecosystem. However, achieving that lush underwater paradise often involves a critical question: Do aquarium plants need CO2?

In this comprehensive guide, we will explore the world of aquarium plants and their relationship with carbon dioxide (CO2). We’ll delve into the science behind plant growth, discuss the various methods of adding CO2 to your tank, and provide insights into the plants that can flourish without additional CO2 supplementation. By the end of this guide, you’ll have a clear understanding of whether CO2 is a necessity for your planted tank and how to make informed decisions to create a thriving underwater environment.

Why Do Aquarium Plants Need CO2 (and Should You Add It)?

Aquarium plants, like their terrestrial counterparts, undergo photosynthesis, a fundamental process that allows them to convert light energy into chemical energy, primarily in the form of glucose. CO2 is one of the essential components required for photosynthesis, alongside light and water. During photosynthesis, plants absorb CO2 from the water through tiny pores called stomata in their leaves.

Once inside the plant, CO2 molecules are used in the Calvin Cycle, a series of chemical reactions that produce glucose and other organic compounds. This glucose serves as an energy source for the plant, enabling it to grow, develop, and reproduce. In return, plants release oxygen (O2) into the water as a byproduct of photosynthesis, which benefits fish and other aquatic inhabitants.

How Much CO2 Is There in an Aquarium?

Before we discuss whether to add CO2 to your aquarium, it’s essential to understand the baseline levels of CO2 present in a typical aquarium. CO2 naturally enters an aquarium through several sources, including:

  1. Fish Respiration: Fish release CO2 into the water as a waste product of their respiration. The CO2 levels in your tank will depend on the number and size of fish.
  2. Decomposing Organic Matter: As uneaten food, fish waste, and decaying plant material break down in the aquarium, they release CO2.
  3. Aquatic Plants: During the night, when photosynthesis ceases, aquarium plants undergo respiration, releasing small amounts of CO2 into the water.
  4. Carbonate Hardness (KH) Buffer System: The carbonate hardness of your water (KH) can act as a pH buffer but also influences the equilibrium between dissolved CO2 and gaseous CO2 in the water.

The CO2 levels in an average, non-CO2-injected planted tank typically range from 1 to 10 parts per million (ppm). This concentration is generally sufficient for the majority of low to medium light plants to perform photosynthesis. However, when it comes to more demanding, high-light plants, or if you aspire to achieve exceptionally lush growth and vibrant colors, you might consider supplementing CO2.

Why Do We Have to Add CO2 to Our Aquariums?

Adding CO2 to your planted aquarium is not always a requirement, but it can significantly enhance plant growth and the overall aesthetics of your tank. Here are some reasons why aquarists choose to supplement CO2:

  1. Accelerated Growth: CO2 supplementation can boost the growth rate of aquarium plants, allowing them to flourish more rapidly. This is particularly advantageous if you want to achieve a lush aquascape quickly.
  2. Vibrant Colors: Plants provided with ample CO2 tend to exhibit more vibrant colors. This can add depth and visual appeal to your aquarium.
  3. Healthy Competition Against Algae: When plants grow vigorously due to CO2 supplementation, they can outcompete algae for nutrients. This can help prevent or reduce algae issues in your tank.
  4. Increased Oxygen Production: As plants photosynthesize with CO2, they release oxygen into the water. Elevated oxygen levels are beneficial for fish and other aquatic inhabitants.
  5. Enhanced Photosynthesis: In high-light setups, where plants receive intense illumination, CO2 becomes a limiting factor for photosynthesis. Supplementing CO2 ensures that this crucial process can occur at its maximum potential.

While CO2 supplementation offers numerous benefits, it’s not without challenges and considerations. The decision to add CO2 to your aquarium should depend on your plant selection, lighting, and your goals for your planted tank. Understanding the needs of your aquatic plants and striking the right balance is essential for creating a thriving aquatic ecosystem.

Aquarium Plants That Do Well Without Additional CO2

It’s important to note that not all aquarium plants require CO2 supplementation to thrive. Many aquatic plants are well-suited for low-tech setups, where CO2 levels are derived from natural sources in the tank. Here are some plant species known for their ability to flourish without additional CO2:

  1. Java Fern (Microsorum pteropus): Java Fern is a hardy and versatile plant that can thrive in low to medium light conditions. It attaches itself to driftwood or rocks and absorbs nutrients directly from the water. This makes it an excellent choice for aquariums without CO2 injection.
  2. Anubias (Anubias spp.): Anubias plants are known for their robust nature and resistance to a wide range of water conditions. They grow slowly, which means they have lower CO2 requirements. Their broad leaves can provide shade, reducing light for potential algae growth.
  3. Cryptocoryne (Cryptocoryne spp.): Cryptocoryne plants are adaptable and can grow in low to medium light setups. They are root feeders and can draw nutrients from the substrate, which makes them suitable for non-CO2-injected tanks.

These are just a few examples of aquarium plants that can thrive without additional CO2. However, keep in mind that while these plants can survive, their growth may not be as fast or lush as in CO2-enriched environments. If you’re seeking rapid, vibrant growth, especially for more demanding plant species, you may want to explore CO2 supplementation methods.

Cheapest DIY Way to Add CO2

If you decide to venture into CO2 supplementation, you’ll discover various methods to add CO2 to your aquarium. One of the most affordable options is a DIY yeast-based CO2 generator. Here’s how to set up a simple DIY CO2 system:

  1. Materials Needed:
    • A plastic bottle (0.5 to 2 liters)
    • A CO2 diffuser or airstone
    • Airline tubing
    • Sugar
    • Active dry yeast
    • Warm water
    • Check valve (optional but recommended)
    • Bubble counter (optional)
  2. Procedure:a. Drill a hole in the bottle cap, making sure it’s just large enough to snugly fit the airline tubing.b. Attach the airline tubing to the cap and secure it with silicone or epoxy to prevent air leaks.c. Fill the bottle halfway with warm water.d. Add sugar to the water, leaving about 2 inches of space at the top of the bottle.e. Add a teaspoon of active dry yeast to the bottle.f. Attach the other end of the airline tubing to your diffuser or airstone inside the aquarium.g. Place the bottle upside down inside your tank, submerging the diffuser or airstone.h. As the yeast consumes sugar, it will produce CO2, which will bubble through the diffuser and dissolve into the water.i. You can use a bubble counter to monitor the rate of CO2 injection and adjust it as needed.

This DIY CO2 system provides a cost-effective way to increase CO2 levels in your planted tank. However, it requires regular maintenance, as you’ll need to replace the yeast-sugar mixture every one to two weeks when CO2 production diminishes.

Advanced Way to Add CO2 to Your Tank

For aquarists seeking more precise control over CO2 levels and stability, advanced CO2 injection systems are available. These setups typically include a pressurized CO2 tank, a regulator, a solenoid valve, a bubble counter, and a diffuser. Here’s how an advanced CO2 system works:

  1. Pressurized CO2 Tank: The pressurized CO2 tank contains compressed carbon dioxide gas.
  2. Regulator: The regulator reduces the high pressure from the CO2 tank to a controlled, low working pressure.
  3. Solenoid Valve: The solenoid valve allows you to automate CO2 injection by connecting it to a timer. This ensures that CO2 is only injected during the lighting period when plants can effectively utilize it.
  4. Bubble Counter: The bubble counter measures the rate of CO2 injection in bubbles per minute (BPM).
  5. Diffuser: The diffuser or reactor disperses CO2 into the aquarium water in small bubbles, maximizing its dissolution.

This method offers precise control over CO2 levels, making it suitable for high-tech planted tanks with demanding plants. However, it requires an initial investment and regular monitoring to maintain CO2 levels within the desired range.


In the quest to create a thriving planted aquarium, the question of whether aquarium plants need CO2 is an important one. Understanding the role of CO2 in photosynthesis and its impact on plant growth is key to making informed decisions for your aquarium.

While CO2 supplementation can significantly enhance plant growth and the overall aesthetics of your tank, it’s not always necessary. Many aquarium plants, such as Java Fern, Anubias, and Cryptocoryne, can thrive without additional CO2.

Ultimately, the decision to add CO2 to your aquarium should be based on your plant selection, lighting, and your goals for your planted tank. Whether you choose a DIY CO2 system or an advanced injection setup, maintaining the right balance of CO2 is essential for creating a lush, vibrant underwater paradise in your aquarium.

Is a CO2 System Necessary for a Large Aquarium?

When considering the size of aquarium needed for a large setup, it is important to consider whether a CO2 system is necessary. In the case of a large aquarium, where plants are abundant, a CO2 system can be highly beneficial. CO2 injection aids in promoting plant growth and prevents algae buildup, ensuring a vibrant and healthy ecosystem within the aquarium. Ultimately, the decision to incorporate a CO2 system depends on the specific requirements of the plants and the desired level of maintenance for the aquarium.


1. Can aquarium plants grow without CO2?

Yes, many aquarium plants can grow without additional CO2 supplementation. However, their growth rate and vibrancy may be limited compared to plants in CO2-enriched environments.

2. Is DIY CO2 injection effective for a planted tank?

DIY CO2 injection can be effective for small to medium-sized planted tanks. It’s a cost-effective method but requires regular maintenance.

3. How do I measure CO2 levels in my aquarium?

You can measure CO2 levels using a drop checker, which changes color based on the CO2 concentration. Alternatively, electronic CO2 monitors are available for more precise readings.

4. Can high CO2 levels harm fish in my aquarium?

Excessively high CO2 levels can harm fish by reducing oxygen availability. It’s essential to monitor CO2 levels and ensure they remain within a safe range for your aquatic inhabitants

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