When and how do you use an aquarium CO₂ system?

CO₂ is kind of the secret sauce of a beautiful planted aquarium. But honestly... the first time I started (with a homemade yeast bottle and a Coke cap), my living room looked more like a hot tub than an aquascape. 😅 Don't panic: it really doesn't have to be that complicated. In this article, I'll tell you exactly when you need CO₂ and how to use it smartly and safely.

CO₂ is especially useful in tanks with bright light and fast-growing plants. Use a pressure-regulated system with a cylinder, pressure regulator, check valve, hose, and diffuser. Start slowly (e.g., ~1 bubble/sec), aim for 20–30 ppm CO₂ (green drop checker), and only run the CO₂ during the day. Don't want to use cylinders and hoses? Liquid alternatives are available.

What does CO₂ actually do for your aquarium plants?

Plants use CO₂ during photosynthesis to produce sugars. In low-light tanks, natural CO₂ (≈2–3 ppm) is often sufficient. However, if you hang strong lighting above your tank or grow fast-growing plants (e.g., Rotala , Monte Carlo ), plants require more carbon than is naturally available. Without additional CO₂, growth stagnates, and algae gain a head start. With a CO₂ system, you accelerate growth, keep leaves healthy, and limit algae.

How does a CO₂ system work step by step?

Cylinder & pressure regulator: the cylinder supplies CO₂; the regulator reduces it to a stable, safe working pressure.
Non-return valve: prevents water from flowing back towards the regulator (always install).
Bubble counter: this allows you to count bubbles and build up your dose gradually (start slowly and adjust weekly).
Diffuser: dissolves CO₂ into fine bubbles. Place it low in the tank or use an inline diffuser for maximum efficiency.
Timer & solenoid valve: CO₂ on at the same time as the light; off at night (plants don't use CO₂ then).
Dropchecker: blue = too little, green = good (≈20–30 ppm), yellow = too much.

Pro tip: Increase the dosage gradually over several days. Increasing the dosage too quickly can cause fish to gasp at the surface (too much CO₂ → oxygen stress).

Common Mistakes (and How to Fix Them)

No check valve: Risk of water damage to your regulator. Always install a check valve.
Too much CO₂: keep the drop checker green; solid yellow = reduce. Target range: ≈20–30 ppm.
DIY yeast for large batches: unstable; save this for nano/micro batches. For larger batches: use a pressure cylinder.
CO₂ without nutrients: works moderately; always combine with a complete plant food and sufficient water flow.

Alternatives to CO₂ systems

Don't feel like dealing with hoses or cylinders? This is also an option:

Liquid carbon (EasyCarbo/Excel): based on glutaraldehyde. Useful in low- and mid-tech tanks and as an algae inhibitor, but not a true CO₂ replacement for high-tech tanks.
Beware of sensitive species: Vallisneria and some mosses can "melt" with (too high) doses of liquid carbon. Start halfway and observe.
More fast-growing species: Species like Limnophila and Hygrophila help algae outcompete, even without the gas CO₂.

Checklist

Do you have a lot of light and demanding plants? → CO₂ is recommended.
Complete set: cylinder, pressure regulator, non-return valve, (inline) diffuser, bubble counter.
Start slowly (~1 bell/sec) and build up; keep an eye on the fish and plants.
Dropchecker green (≈20–30 ppm); CO₂ on in light, off in dark.
Alternative: liquid carbon + complete plant food.

Conclusion

CO₂ isn't a magic potion, but it is the ultimate boost for strong plant growth and less algae. With a stable dosage (≈20–30 ppm), good nutrition, and appropriate lighting, your tank will become an underwater jungle. Not sure about your setup? Feel free to send us a message or app to 📲 06-1823814 — we're happy to help!