How To Add Co2 to Aquarium

Aquariums are beloved by hobbyists and enthusiasts for their colorful fish and lush underwater plants. To create a thriving environment for your aquatic creatures, you need to pay close attention to their needs. One essential element that plays a big role in the health and vibrancy of your aquarium is carbon dioxide (CO2). 

In this blog post, I’ll delve into why CO2 is so important for your aquarium, how to keep safe CO2 levels for your fish and plants, the benefits of CO2 in a planted aquarium, and the different proven methods to add CO2 to aquariums. 

But before we explore how to add CO2 to your aquarium, let’s first understand why your aquarium needs CO2. So let’s get started

Why is CO2 Necessary for My Aquarium?

Your aquarium needs carbon dioxide (CO2) for the plants that live underwater. Just like plants on land, underwater plants also go through a process called photosynthesis. This is when they use CO2 and light to make their own food and grow. CO2 is like food for these plants, crucial for their growth and overall health.

Enough CO2 in your aquarium helps the plants grow strong and healthy. When the plants thrive, they create a beautiful and natural environment for all the fish and other creatures in your aquarium. So, providing enough CO2 is essential to keep your aquatic habitat looking vibrant and lively.

How Much CO2 is Safe for an Aquarium?

Having the correct amount of CO2 in your aquarium is really important because if there’s too little or too much, it can cause problems for the creatures living there. If you have plants in your aquarium, it’s essential to ensure they get enough CO2 to grow well, but not too much that it becomes harmful.

For a tank with plants, the ideal CO2 level is between 20 to 30 parts per million (ppm). This means there should be 20 to 30 CO2 molecules for every one million molecules of water in the tank. Maintaining this balanced CO2 level helps the plants to flourish and keeps the water healthy for your fish and other aquatic friends.

To ensure you have the right CO2 level, you can use a CO2 testing kit. This kit helps you regularly check the CO2 levels in your aquarium. If you find that the levels are not in the safe range, you can make adjustments to keep everything balanced and ensure a happy and thriving underwater home for your aquatic buddies.

Now that you’ve grasped the reasons why your aquarium requires CO2 and how to ensure a safe CO2 level for it, let’s delve into the advantages of using CO2 in a planted aquarium

The Benefits of CO2 in a Planted Aquarium

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1. Faster Plant Growth And Improved Plant Health

When there’s lots of CO2, plants can make their food more efficiently, which makes them grow lush and vibrant with strong, healthy leaves. This fast growth is great when you’re starting an aquarium with plants or adding new ones. It helps the plants settle in quickly and look beautiful in your aquarium.

Also, having enough CO2 helps keep the plants healthy and prevents common problems like yellow leaves (chlorosis). This is because plants get all the resources they need to create important nutrients.

2. Dense Plant Growth

Dense plant growth is beneficial because it helps to prevent excessive algae growth. The plants become strong competitors for nutrients and light, which means there are fewer opportunities for algae to take over and cause problems.

3. Increased Oxygen Production 

When plants do photosynthesis (their way of making food), they take in carbon dioxide (CO2) and give out oxygen as a result. This extra oxygen production is great for the creatures living in the aquarium, like fish and other water-dwelling animals. 

Having more oxygen makes the aquarium environment healthier for them, and they can breathe better. So, it’s like the plants are helping to keep the water fresh and comfortable for all the aquatic life in the tank.

4. Stable pH Levels

Sometimes, adding carbon dioxide (CO2) to an aquarium can help keep the water’s pH level stable. This is especially true if you have soft water and not much natural ability to balance pH (called carbonate buffering capacity). 

The CO2 can work like a helper, preventing the pH level from getting too high or too low, and keeping it more steady. This stability is good for the well-being of the aquarium’s inhabitants, as sudden pH changes can stress them out.

In a planted aquarium, adding carbon dioxide (CO2) can be really good for the health and growth of aquatic plants. It helps them grow better. But we need to be careful because too much CO2 can be bad for the fish and other creatures in the aquarium. 

It can make them stressed, and sick, or even cause them to die. So, let’s find out the right way to add CO2 to your aquarium.

Ways To Add CO2 To Aquarium

1. Passive CO2

Passive CO2 supplementation is a simple and affordable way to add CO2 to smaller aquariums or tanks with plants that don’t need a lot of light. Instead of using equipment, this method relies on the natural activities happening inside the aquarium. 

Fish and plants naturally release some carbon dioxide as they breathe, and when organic matter breaks down, it also contributes to CO2 production. While this method can provide a basic amount of carbon dioxide, it might not be enough for plants that require a lot of CO2 to grow well.

2. Yeast-Based Systems

Yeast-based CO2 systems are well-liked by aquarium hobbyists who have smaller to medium-sized tanks. This method involves a do-it-yourself setup where you create a mixture of yeast, sugar, and water in a container connected to your aquarium through a tube.

As the yeast consumes the sugar, it releases CO2 gas, which then gets diffused into the water using a basic airstone or a reactor. The best part is that yeast-based systems are budget-friendly and quite simple to set up.

But here’s the catch – since yeast is a living organism, the amount of CO2 it produces can vary depending on its activity. That’s why it’s crucial to keep an eye on CO2 levels regularly. You want to make sure your plants get a steady and consistent supply of CO2 for healthy growth. 

Monitoring the yeast activity and adjusting the setup as needed will help you maintain stable CO2 levels and provide the best care for your aquatic plants. So, if you enjoy some DIY fun and have a smaller aquarium, a yeast-based CO2 system might be just the right choice for you.

3. Aerosols

CO2 aerosols, which are also called liquid CO2 or carbon sources, are a convenient choice for aquariums with plants that don’t need a lot of carbon dioxide. These products usually contain liquid carbon in the form of glutaraldehyde or similar substances.

When you add them to the aquarium, they become an extra source of carbon for the plants, along with the CO2 produced by the fish and natural processes.

These aerosols can be really helpful for the growth of your plants, especially if you have an aquarium with low to moderate plant needs. They provide an additional boost of carbon that can enhance the health and vitality of your aquatic greenery. 

However,  if you have a heavily planted tank with plants that demand a lot of CO2, these aerosols may not be enough to meet their requirements.

In such cases, you might need to consider other CO2 supplementation methods like DIY CO2 or pressurized CO2 systems to ensure your high-demanding plants get the carbon they need for robust growth.

4. DIY CO2 Systems

DIY CO2 systems provide a better way to control and maintain CO2 levels compared to yeast-based setups. With this method, you create CO2 in a reaction chamber using citric acid and baking soda or other combinations. 

The generated CO2 gas is then directed into the aquarium through a diffuser. The great thing about DIY CO2 systems is that they can be customized to suit the size of your aquarium, and you can adjust the reaction rate to manage CO2 levels more precisely.

However, it’s important to know that DIY CO2 systems need regular attention and upkeep to ensure a steady supply of CO2. You’ll have to monitor the setup consistently to make sure the CO2 levels remain stable and within the required range for your plants. 

But with proper maintenance, DIY CO2 systems can be an effective and economical solution for promoting healthy plant growth in your aquarium.

5. Pressurized CO2

Pressurized CO2 systems are a complete setup with different parts: a CO2 cylinder, a regulator, a solenoid valve, and a diffuser. The CO2 cylinder holds the carbon dioxide under pressure, and the regulator controls how much CO2 goes into the aquarium. 

This keeps the CO2 levels stable and just right for your plants. The solenoid valve acts like a switch, turning the CO2 flow on and off at specific times. It’s handy for automating the process and saving CO2 when your plants don’t need it, like during the night.

These pressurized CO2 systems offer excellent control and stability. That means your plants will always have the perfect amount of CO2 to grow and thrive.

Although they might cost more initially than other methods, they are a worthwhile investment for serious aquarium enthusiasts who want to create a beautiful and flourishing underwater paradise. 


To have a happy and thriving aquarium that makes fish and plant enthusiasts happy, it’s essential to take care of the needs of your underwater creatures. One crucial element for their health is carbon dioxide (CO2).

In this blog post, we learned why CO2 is so important for your aquarium and how to make sure there’s a safe amount of it for your fish and plants. CO2 is especially beneficial for a planted aquarium, making it more beautiful and functional.

We also talked about different ways to add CO2 to your tank, so you can choose the best method for your setup. By using the right CO2, you can create a magical underwater paradise for your aquarium.


How to Add CO2 with Aquarium Chemicals?

Adding CO2 to your aquarium is vital for fostering robust plant growth and maintaining an ecologically balanced environment. Aquarium chemicals provide an efficient means of supplementing CO2. To ensure successful CO2 addition, follow this step-by-step guide:

First, choose a suitable CO2 supplement, such as liquid additives or CO2 tablets, based on your tank size and plant needs. Next, adhere to the manufacturer’s guidelines carefully to avoid any harm to your fish or plants.

Timing is crucial; add CO2 during the morning or when the aquarium lights are on to coincide with active plant photosynthesis. Lastly, monitor the effects and make gradual adjustments to the dosage as needed for a stable and thriving aquarium ecosystem.

When Should You Add CO2?

In order to maximize the advantages of adding CO2 to your aquarium, it’s crucial to choose the right time for its introduction. The best approach is to align CO2 dosing with your aquarium’s light cycle. This means adding CO2 when the lights are on and turning it off when the lights are off. 

By doing so, the plants can utilize the CO2 effectively during their active photosynthesis period. Avoid adding CO2 at night, as plants do not undergo photosynthesis then, and excess CO2 during this time can cause pH fluctuations and stress your fish.

To ensure your aquatic plants thrive, establish a consistent CO2 dosing schedule, as fluctuating CO2 levels can be harmful to their health.

Is There a Way to Measure CO2?

You can measure CO2 in your aquarium using two methods: a drop checker and CO2 test kits. The drop checker changes color with the amount of CO2 in the water, giving you an idea of the CO2 levels. The CO2 test kits work by testing a water sample with liquid reagents and a color chart to determine the CO2 concentration. 

It’s important to regularly check CO2 levels to avoid issues like poor plant growth due to low CO2 or harm to your fish from too much CO2. Make sure to find the right CO2 amount for your plants and maintain a good balance of light, fertilization, and water quality for a healthy aquarium.

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