Yes, an imbalance between CO2, light, and nutrients can lead to algae outbreaks. See our guide for treating aquarium algae.

CO2 Systems Guide for Aquariums

Why install a CO2 system in your aquarium?

To ensure optimal growth of certain aquatic plants, CO2 injection is often essential. This is particularly true for red-colored species like Ludwigia palustris Super Red, or for carpeting plants used in aquascaping.
CO2 injection also slightly lowers the water’s pH, which is especially beneficial for fish that prefer soft, acidic water, such as discus.

Budget solution

Uses a CO2 fire extinguisher.

See details

Intermediate solution

Balance between performance and price with ready-to-use kits.

See details

Premium solution

High-end systems with precise electronic control.

See details

No-install solution

For very small budgets, not recommended

See details

Budget solution

Here are the components, pros, cons, and step-by-step tutorial for setting up a low-cost extinguisher-based solution.

Image	Component	Link
	CO2 extinguisher (2kg or 5kg) w21.8 Warning: 5kg may be too tall if you have a small cabinet.	View on Amazon (2kg) View on Amazon (5kg)
	CO2 regulator with solenoid valve w21.8	View on Amazon
	CO2 tubing	View on Amazon
	CO2 diffuser (glass)	View on Amazon
	Optional: bubble counter	View on Amazon
	Optional: programmable outlet	View on Amazon

Assembly in 4 Steps

1. Screw the valve/regulator onto the extinguisher nozzle. Check for leaks using soap.

2. Connect the tubing to the valve and run it over the top of the aquarium to the diffuser.

3. Plug the solenoid valve into a socket, ideally programmed to turn on with the lighting if you included a programmable outlet.

4. Adjust the CO2 flow with the bubble counter by gently turning the knob (go slowly): one bubble every 2–4 seconds is a good start.

Average cost between €100 and €160

Click here if you want more information on choosing a CO2 extinguisher for your aquarium

Advantages

Cost-effective over time
Modular and upgradeable
Great for small budgets
Easy to buy/refill extinguisher

Disadvantages

Requires a bit of DIY
Not always visually appealing

Video Tutorial: Installing a Budget CO2 System

Follow our complete video guide to learn how to install a CO2 system using a fire extinguisher in your aquarium. This simple and economical method is perfect for beginners and aquascaping enthusiasts alike.

Watch the full video on YouTube: Budget Aquarium CO2 Tutorial (Extinguisher Installation)

Tip: Once your extinguisher-based CO2 system is installed, be sure to test your water (pH and CO2) to fine-tune the flow rate. Too much CO2 can harm pH balance and your fish.

See our CO2 testing tutorial

Still hesitating between options?

If you're ready to invest a bit more for easier installation, our intermediate solution with a complete kit might suit you better.

And if you're looking for full comfort with automation, safety, and precision, the premium CO2 solution is made for you.

Intermediate Solution

Details of the ready-to-use gear, installation, cost, and performance for serious aquarists.

This complete CO2 kit includes everything you need: bottle, regulator with solenoid valve, bubble counter, and diffuser. A balanced solution between simplicity and performance.

View on Amazon

Average cost: €140

Advantages

Affordable solution
Suitable for small budgets

Disadvantages

Often expensive in the long run since the bottles must be replaced completely when empty

Good to know: Even with a ready-to-use kit, monitoring water quality is essential. The goal: avoid excess CO2 to keep fish and plants healthy.

Check out our CO2 testing guide

Still unsure?

If the intermediate kit seems simple but you're looking for something even more automated, check out our guide on the premium CO2 solution with full electronic control.

On the other hand, if your priority is cutting costs while maintaining efficiency, explore our budget extinguisher-based solution, a favorite among low-tech enthusiasts.

Premium Solution

A high-end setup, often used in aquascaping or heavily planted tanks. Everything is automated: safety, stability, and maximum comfort.

This kit includes a refillable CO2 cylinder, dual gauge regulator, solenoid valve, bubble counter, high-efficiency diffuser, drop checker, and automated pH controller.

View on Amazon

Average cost: €320

You can also add a real-time monitoring computer:

View on Amazon

Average cost: €200

Advantages

All-in-one with automation
Precision and maximum comfort
Refillable cylinder
Ideal for demanding tanks

Disadvantages

High cost
More technical to install

Recommendation: Premium systems are precise, but it's still recommended to occasionally monitor your water for perfect CO₂ management.

Learn how to test your water effectively

Looking for more affordable options?

If you want a more affordable solution with good performance, our intermediate kit is a great compromise.

For DIY enthusiasts or small budgets, the budget extinguisher-based version remains very popular.

Don’t forget: even the best CO2 system doesn’t replace proper monitoring. Test your parameters regularly to avoid imbalances.

No CO₂ Solution

A workaround for very limited budgets.

This liquid carbon allows you to add "liquid CO₂" to your tank.

View on Amazon

Average cost: €13

Advantages

Very budget-friendly solution

Disadvantages

Often costly in the long term
Must be added daily to the tank
Liquid carbon will never fully replace real gaseous CO₂

Warning: Keep control of your tank’s health when using carbon additives.

Read our guide on CO₂ testing

CO₂ Kit for Nano Aquariums

A compact, efficient, and easy-to-install system designed for aquarists with small tanks (10 to 30 liters). See our CO₂ guide for nano aquariums

This CO₂ kit for nano aquariums includes a 95g disposable cartridge, a compact regulator with fine adjustment, a diffuser adapted for small tanks, and a mounting bracket. Perfect for starting out without overwhelming your setup.

View on Amazon

Average cost: €80–100

Advantages

Ultra-compact format, ideal for small aquariums
Quick setup, no DIY required
Fine flow adjustment possible, even at low volumes

Disadvantages

Limited autonomy (1 to 2 months depending on usage)
Replacing cartridges can be more expensive in the long run

Good to know: In nano tanks, balance is more fragile. It’s strongly recommended to use a drop checker and monitor pH regularly to avoid CO₂ overdosing.

Check out our guide on CO₂ and pH testing

Need an alternative?

If you prefer an even simpler option without cartridges, you can explore DIY CO₂ kits based on yeast, ideal for beginners in low-tech aquariums.

Conversely, for more advanced management in your nano tank, the premium solution with electronic control can be useful even on small volumes.

Can CO2 cause algae?

Yes, an excess or imbalance of CO2 can promote algae growth. This especially happens if the lighting is too strong or if other nutrients (such as nitrates or phosphates) are unbalanced.

To avoid this, it is important to regularly test your water and adjust the CO2 injection precisely.

Once your CO2 system is installed, monitoring water quality is essential to prevent imbalances and the risk of algae or bacterial growth. Discover our guide on aquarium water testing (test strips, drop tests, and digital tests) to learn how to correctly analyze your parameters.

Frequently Asked Questions about CO2 in Aquariums

What is the role of CO2 in a planted aquarium?

CO2 promotes plant photosynthesis, making them healthier, denser, and more vibrant.

Can a fire extinguisher be used as a CO2 source?

Yes, it is a widely adopted economical solution. You need a compatible regulator (W21.8) and good flow control.

Is CO2 dangerous for fish?

In excess, yes. Poorly controlled CO2 can lower pH or suffocate fish. Regular water testing is necessary.

Is there an alternative to bottled CO2?

Liquid carbon is a partial alternative, convenient for small tanks, but less effective than a pressurized CO2 system.

Can CO2 cause algae?

Yes, especially if poorly dosed or poorly synchronized with lighting. A good balance of light, nutrients, and CO2 is essential. If you notice algae growth (brush, filamentous, brown...), consult our comprehensive guide to identify and effectively remove them.