CO2 plays a crucial role in creating a healthy, vibrant aquarium environment, especially in planted tanks. If you’re looking to enhance your plant growth, promote a balanced ecosystem, and even reduce algae growth, understanding how to use CO2 effectively is key. While adding CO2 can dramatically boost plant growth by a big amount, it’s not strictly necessary for a thriving aquarium. Many plants will do perfectly well in a tank that has sufficient nutrients and the correct lighting, though certain species may benefit significantly from supplemental CO2.

In this guide, we’ll break down everything you need to know about CO2 in aquariums and how it can benefit both your plants and fish.

 

1. What Is CO2?

CO2 (carbon dioxide) is a colourless, odourless gas that is essential for plant life. In your aquarium CO2 is used by plants during photosynthesis to produce energy, which is critical for their growth and overall health.

In your aquarium the primary goal of adding CO2 is to boost plant growth and improve the overall balance in your tank, this is done by providing your plants with the necessary carbon they need so they can grow and thrive.

 

2. Why Add CO2 to Your Tank?

There are several key benefits to adding CO2 to your aquarium:

 

Boosts Plant Growth:

Plants use CO2 to carry out photosynthesis, which is how they make their food. With a steady supply of CO2 it boosts photosynthesis and gives them more food to consume which is why plants will grow more quickly and healthily.

 

Improves Plant Health:

Healthy plants compete with algae for nutrients like nitrates and phosphates. This can reduce the likelihood of algae taking over your tank.

 

Helps Maintain Stable pH:

CO2 can help maintain a more stable pH level in your tank. It works with your aquarium’s natural buffering capacity to create a balanced environment for your fish and plants.

 

• Pro Tip: If you notice your plants are growing slower than usual or showing signs of yellowing leaves, it could be a CO2 deficiency! Adding CO2 can often resolve these issues and jumpstart your plant growth in no time, but be careful! Too much CO2 saturation can also cause yellowing leaves and plant death.

 

3. How to Add CO2 to Your Aquarium

There are several methods for introducing CO2 into your aquarium, depending on the size of your tank and your goals:

 

1. CO2 Gas Injection System:

The most efficient and commonly used method for larger tanks or tanks with high plant density and growth.

It involves a CO2 cylinder, regulator, solenoid, bubble counter, air hose tubing, a drop checker, and a diffuser to distribute the CO2 into the tank.

CO2 injection is best suited for aquariums over 75 litres for beginners but those with a more advanced aquascape knowledge can use it in as low as 20-40 litres but this requires much more care and precise gas exchange measurements to keep the small tanks in balance.

 

• Tip: When setting up a CO2 gas injection system, consider placing the CO2 diffuser in a high flow area to help distribute CO2 evenly throughout the aquarium. Inline kits can also be purchased that allows you to connect your CO2 kit to the outtake of a canister filter, this will cause the gas to be blown through the out flow of your canister filter giving out an even CO2 coverage in your aquarium.

 

• Pro Tip: Plug the solenoid into a timer adapter and set the timer to turn on about 2 hours before the lights in your aquarium turn on and set it to turn off 1 hour before the lights go out, this will make your CO2 start the gas exchange process as the lights come on and off mimicking the plants natural cycle. This is important because plants stop absorbing CO2 during the night and release oxygen instead, so keeping your CO2 on during the night can over saturate your tank and cause harm to fish.

 

• Tip: keep an eye on the fish in your aquarium, if you see any signs of stress such as darting, erratic behaviour or gasping at the surface, you may need to turn your CO2 down and/or fix its operating hours!.

 

2. CO2 Liquid Additives:

Liquid CO2 is a more affordable option for smaller tanks or beginners.

Liquid solutions like Flourish excel (although some believe excel is more of an algaecide/algae killer than a CO2 solution) or API CO2 Booster are designed to provide your plants with the necessary carbon in a more straightforward form, though they are generally a lot less effective than a CO2 gas system.

 

• Pro Tip: Liquid CO2 is a good choice for tanks with slow-growing plants or if you're just starting with CO2. You can always upgrade to a gas or DIY system later as your tank’s needs to evolve.

 

3. DIY CO2 System:

DIY kits can be a very budget-friendly option, especially for smaller tanks.

This system can use ingredients such as yeast, sugar, and water to generate CO2 gas. Ingredients such as citric acid, baking soda and water can work just as well.

This method is ideal for hobbyists looking for a simple and inexpensive solution.

 

 

• Tip: DIY CO2 systems can be a fun and cost-effective way to experiment with CO2 in smaller tanks. However, they can be less stable than commercial systems, so be prepared for some trial and error while adjusting CO2 levels.

 

• Pro Tip: I personally run a DIY CO2 system in my home aquarium. I use the citric acid, baking soda and water method. While it’s an affordable option, I’ve found that the CO2 levels can fluctuate more than with a commercial system, so it requires a bit of monitoring and quiet a bit of adjustment. It’s not as “set it and forget it” as gas injection can be, but it’s a great entry-level way to add CO2 and see how it impacts your plant growth, I have personally seen quite an improvement on my plants since I started my DIY experiment!

 

4. How Much CO2 Does My Tank Need?

The right amount of CO2 depends on several factors, such as the size of your tank, the number of plants, and the lighting you provide.

 

Here’s a quick guide:

 

Low-Tech Tanks:

For tanks with slower-growing plants such as Anubias or have lower lighting, a CO2 level around 10-15 ppm (parts per million) is sufficient. 

 

• Tip: You can adjust the rate at which CO2 is injected into your tank by turning the regulator to increase or decrease the flow of bubbles in your bubble counter. As a general guideline, most tanks on average require 1-2 bubbles per second (BPS) but again this can vary depending on factors such as tank size, plant density and lighting.
  

 

• PLEASE NOTE: Do not add in too much too fast, TAKE IT SLOW!. start at 1 Bubble per second (BPS) and adjust it when needed, too much too fast can suffocate your tank leading to plant and fish DEATH!.

 

• Pro Tip: If you’re unsure about your CO2 levels, start with a lower dosage and gradually increase it. Watch your plants for signs of improvement or stress, and adjust accordingly.

 

High-Tech Tanks:

For tanks with fast-growing plants and high-intensity lighting, you’ll need a higher CO2 level, around 20-30 ppm or more.

 

• Pro Tip: Due to bubble per second (BPS) varying so much it is best to use a CO2 drop checker to monitor your CO2 levels more accurately. This tool helps you maintain a stable range of CO2 in your tank by showing you exactly how much CO2 ppm is dissolving in your aquarium indicating to you whether or not you should turn it up or down ensuring your plants receive the right amount of CO2 and thrive without harming your fish. 

 

• Tip: Drop checkers are best to be placed on the opposite side of the aquarium from where your CO2 diffuser is pushing bubbles into yout tank, but make sure it is still getting some flow so it can get an accurate CO2 reading throughout the whole aquarium. The checker should change between 3 colours, BLUE, GREEN, and YELLOW. Blue means you are not putting enough CO2 into the tank and it needs to be turned up!. Green is the sweet spot and means you do not need to add any more or any less!. Yellow is entering the danger zone and you may need to turn your CO2 down a little.

 

•  PLEASE NOTE: The drop checker changes roughly every 2 HOURS!. So it is best to make sure you are keeping an eye on it and adjusting your CO2 accordingly, once adjusted wait another 2 HOURS and see if the drop checker has changed colour in any way, once it turns green your all set!.

 

5. CO2 and Algae: How Does CO2 Help?

CO2 and algae control are closely connected. While CO2 doesn’t directly eliminate algae, it plays an indirect but powerful role in helping plants grow healthier and stronger which can help control algae.

 

Healthy Plants Outcompete Algae:

Plants that grow faster and stronger will absorb more nutrients thus leaving fewer resources for algae to feed and thrive on and lowers the chances of algae overgrowth.

 

Better Light Absorption:

Thriving plants also have the ability to absorb more light, which means less light reaches the algae. Some algae thrive in well lit environments, so keeping your plants healthy and robust will naturally limit unwanted algae growth.

 

• Pro Tip: If you’re dealing with persistent algae, try increasing your CO2 levels slightly. This may help your plants outcompete the algae for nutrients.

 

6. Potential Risks of CO2 Injection

While CO2 can offer significant benefits to your aquarium, it’s important to manage it carefully!. Too much CO2 injection can cause problems in your aquarium, especially for fish.

 

CO2 Toxicity:

An excess of CO2 can lower your aquarium’s pH too much, leading to an environment that’s too acidic for your fish. This can cause stress, gasping for air, or even death in extreme cases.

 

• Tip: To avoid CO2 overdose, always start slowly and monitor your fish for signs of stress. Most say to start at 1 BPS and make adjustments as necessary to maintain a safe, balanced environment.

 

Fish Sensitivity:

Some fish species are more sensitive to pH changes caused by CO2 injection. Make sure the fish in your tank are compatible with CO2 levels before implementing a system.

 

• Pro Tip: If you have sensitive fish, such as freshwater shrimp or certain species of tetras, keep a close eye on your CO2 levels and consider using a regulator with precise control to prevent swings in CO2 concentration.

 

7. Maintaining CO2 in Your Tank

To get the most out of your CO2 system, regular maintenance is key:

 

 

Clean Your Diffuser:

CO2 diffusers can get clogged over time due to algae build up or mineral deposits. Regularly clean your diffuser to ensure efficient CO2 distribution.

 

• Pro Tip: A toothbrush works wonders for cleaning stubborn algae and mineral build up on CO2 diffusers. Just gently scrub the diffuser to keep it in top shape.

 

Monitor CO2 Levels:

Keep track of your CO2 ppm, and make sure it stays in the optimal range for your plants and fish.

 

Check for CO2 Leaks:

Always check your CO2 system for leaks, especially if you use a gas injection system, as a CO2 leak can affect your tank’s overall balance.

 

• Pro Tip: If you're using a CO2 gas system, check the CO2 cylinder regularly. Be sure you’re aware of how long it will last before needing to be replaced or refilled, it's never bad to have a refill on hand for a quick swap out so your CO2 intake stays consistent.

 

8. Should You Add CO2 to Your Tank?

Adding CO2 to your aquarium can significantly improve plant growth, help control algae, and create a more stable, balanced environment for your fish. However, it’s important to use CO2 responsibly and maintain your system properly to avoid any potential issues.

If you have a heavily planted tank or want to take your aquascaping to the next level, CO2 injection is an excellent investment. But even if you're just starting, adding a simple liquid CO2 additive can still give your plants the boost they need and help reduce algae.

 

• Pro Tip: If you’re new to CO2 systems, start with a simple liquid CO2 solution and monitor the results. You can always upgrade to a more advanced system later as your aquarium needs evolve.

 

By following these tips and monitoring your CO2 levels, you’ll create a thriving, beautiful tank that both you and your fish can enjoy!

 

 

 

What is This Green Stuff in My Tank? A Guide to Algae and How to Maintain It.

While CO2 can certainly help promote healthy plant growth and improve the balance of your aquarium, algae can still be an issue if nutrient levels aren’t properly managed. If you're noticing unwanted algae growth despite using CO2, it's important to address the root causes!

For more tips on controlling algae and maintaining a healthy aquarium ecosystem, be sure to check out our guide to algae and how to maintain it blog! It covers everything from identifying different types of algae to implementing effective solutions.