CO2 system aquarium: What to look for before you buy

It’s happening: you’re buying a CO2 system for your aquarium. Great move, because a proper CO2 aquarium setup is the foundation of a tank full of lively plants and lush green carpeting. But… what’s the best CO2 system for your fish tank? What should you look for when buying your kit?

The importance of CO2 in your aquarium (can’t stress this enough 🙂 )

CO2 is essential for your aquarium plants. It’s not for nothing that it’s one of the macro-elements needed for plant growth, both in your tank and in nature.

But be careful — the amount of CO2 in your aquarium needs to be exactly right:

• Too much CO2? That’s a problem, because your fish might die
• Too little? Your plants will struggle, or you’ll end up with thread algae, black beard algae, …

So adding CO2 isn’t something you just wing. That’s why a proper CO2 kit for aquarium plants — or CO2 system for fish tank — is a must. Sure, it’s an investment, but hey — you need a bowling ball to bowl, right? Same goes for a thriving aquarium: you need the right CO2 aquarium setup.

A quality CO2 system for fish tank is worth every penny — here’s why

Like I said, a solid CO2 aquarium setup is a real investment, but totally worth it. Honestly, I think it’s the best thing you can buy if you want to take your planted tank to the next level. CO2 helps your plants get the carbon they need straight from the water. If there’s not enough CO2, you’ll end up with a dull, sad, and pale tank. Here are some signs your aquarium might be low on CO2:

• Deformed leaves
• Poor plant growth — or none at all
• Holes in the leaves
• Little to no leaf formation
• Bare or stretched stems
• Loss of color in the leaves
• Algae: thread algae, black beard algae, etc.

Not really what you were going for when you pictured your dream aquascape, right?

Maybe you’ve thought about using bio CO2 or liquid carbon? Those are cheaper options, but in my opinion, not great in the long run:

• Liquid carbon: needs to be added daily and gets expensive over time. Also, not all plants like it;
• Bio CO2: super cheap, but unstable. You have to monitor it constantly, or you might not even notice your tank is out of CO2. In my experience, black beard algae is more common with bio CO2.

That’s why I always go for a CO2 system for fish tank if I’m working with a plant-heavy or more demanding aquarium.

Which CO2 system? And what does a CO2 kit for aquarium plants need to include?

Alright, sounds good — but what kind of CO2 system should you actually buy for your aquarium? Well, the best CO2 aquarium setup is one that suits both your tank and yourself. But regardless of the exact setup, some components are essential. Others? Optional.

You absolutely need:

• A high-quality needle valve: You want precise control over the number of CO2 bubbles you inject per second. A reliable needle valve helps you dial things in perfectly. In my view, it’s the most important part of the CO2 aquarium setup.

• An integrated solenoid valve: Plants don’t use CO2 at night. A solenoid valve prevents you from adding CO2 at night, saves a bunch of CO2, and helps oxygenate the tank. I personally like one that’s mounted directly between the CO2 pressure regulator and the needle valve.

• A CO2 regulator for fish tank. Your aquarium regulator needs to bring the pressure down to the right level — around 1.5 bar. Mount it directly on your CO2 cylinder and choose one that lets you adjust the working pressure easily and is made from solid materials.

• An adapter for a refillable CO2 cylinder: You can use disposable or refillable bottles. Disposable is fine for smaller tanks, but if you’ve got 100L or more, I’d go with refillable. Just make sure there’s a place nearby to get your bottle refilled.

What CO2 cylinder should you choose?

I already mentioned this, but I’m a big fan of the refillable CO2 cylinder. Which one’s right for you? It depends — but here’s my main advice: better too big than too small.

Why? A few reasons:

• Fewer refills means fewer trips when your CO2 suddenly runs out;
• More stable CO2 levels, since your bottle won’t run empty as fast. Every refill creates a short-term drop in CO2 — unless you’ve got backups. That means fewer algae issues;
• You’ll feel more at ease not having to constantly wonder if your CO2’s about to run out.

Should you go with a reactor, diffuser, or atomizer in your aquarium with CO2?

To complete your CO2 aquarium setup, you’ll need a device to diffuse that CO2 into the water. Here’s a quick overview of the differences between a diffuser, atomizer, and reactor. Want the full details? Check out this article.

• CO2 diffuser: Want ultra-fine bubbles and sleek glass looks? Go with a diffuser. They come in many shapes and sizes, but they do need good water circulation to work well.

• CO2 atomizer: Great for smaller tanks, and you can find both in-tank and inline versions. Atomizers don’t really create bubbles — more like a mist.

• CO2 reactor: In my opinion, a must for large tanks — but they work well in small ones too. A reactor is super efficient and low-maintenance. You will need a strong filter, but that’s usually already the case with larger setups.

Why you probably shouldn’t go for a cheap CO2 kit for aquarium plants

Like with most things, it’s smarter to invest in a reliable CO2 system for your aquarium from the start. Cheap usually ends up being expensive with CO2 systems… Why? Take a cheap needle valve, for instance — if it’s unstable, you might one day find all your fish dead from a CO2 overdose.

This goes for every part of your CO2 system — aquarium regulator, solenoid valve, diffuser, reactor, you name it. Go for a durable and stable CO2 aquarium setup and you’ll actually get what you paid for. It’ll last way longer and perform the way it should.

Also check the warranty. Lots of cheap CO2 regulators for aquarium setups on certain platforms (not naming names here ;-)) only give 1 year or even 6 months. PlantedBox, though, offers 3 to 10 years depending on the model.

No budget yet for a proper CO2 setup?

Don’t have the cash for a complete CO2 system yet? Slow down photosynthesis by using lower light. You could dim your lights or add some floating plants. That way, your plants grow slower, need less CO2, and the naturally present CO2 in your aquarium might be enough for now. It gives you time to save up for that dream CO2 system.

You can also purposely go for a tank without CO2 — read more about that in this article.

Conclusion

A good CO2 aquarium setup saves you a lot of stress and gives you a bright, algae-free tank. Your plants will thrive and look colorful and full of life — just like your fish, who’ll feel right at home.

So what should you watch out for when buying a CO2 system for your aquarium?

• A quality CO2 regulator with solid solenoid valve and precision needle valve
• Pick the right device: diffuser, atomizer, or reactor?
• Choose a CO2 bottle big enough for your tank — fewer refills!
• No budget yet? Reduce lighting and take your time to choose the right CO2 system for fish tank.

Questions? Feel free to drop them in the comments below!