Does my fish tank need CO2?

I think I get this question almost every week: “Does my fish tank need CO2? And if so, what is the best CO2 setup for my aquarium?”

A CO2 system is a serious investment, so the last thing you want is to buy the wrong one. In this article, you’ll find out whether your aquarium needs CO2 and I’ll share tips to help you choose a good CO2 system.

Aquarium CO2 benefits and importance

Why do planted aquariums need CO2? It all comes down to carbon. Your aquarium plants — just like plants on land — love carbon. It’s one of their main nutrients, a so-called “macro element,” just like nitrate, phosphate, and potassium. In fact, 40 to 45 percent of the “dry weight” of all plants on Earth consists of carbon.

In other words: without carbon, your plants would simply die off.

Is there suddenly a CO2 shortage in your aquarium? Then you’ll quickly notice that your aquascape looks a lot less attractive. You may see algae in the tank, deformed leaves on your plants, or aquarium plants losing color or developing holes. In short, not what you had in mind when you started your aquascape.

Personally, I’m a big fan of CO2 and I use it on all my aquariums. Why? Because it comes with quite a few benefits:

• Greatly reduced risk of algae, especially beard algae and thread algae
• Lush plant growth with vibrant colors and strong roots and stems
• Improved availability of nutrients and trace elements for even healthier growth
• Fewer deformed leaves, less color loss in aquarium plants, and no holes in the leaves

When you see the aquarium CO2 benefits listed like this, it’s easy to understand why CO2 can give a boost to almost any aquarium. I say “almost” for a reason. Even though I generally recommend investing in a CO2 system, it is possible to manage without one.

When does my fish tank need CO2, or not?

To be clear: it is absolutely possible to keep a healthy aquarium without CO2. But there are some conditions. The only way to run a CO2-free aquarium without running into beard algae and thread algae due to CO2 deficiency is to choose:

• An aquarium with few plants
• Weaker lighting
• Fewer light hours per day
• Easy aquarium plants

By choosing weaker light & fewer light hours, you slow down plant growth, which also lowers the demand for CO2. Plus, your aquarium produces CO2 on its own (for example through bacteria in the filter). By deliberately keeping the lighting very low, the naturally available CO2 in your aquarium can stay balanced with what the plants need — especially if you don’t have many plants and stick to easy species.

But what if you love a beautifully lit tank full of special plants? A tank like the one below?

A tank like this has:

• Lots of plants
• Special plants, including sensitive foreground plants and red aquarium plants
• Stronger lighting for compact, attractive growth

Do planted aquariums need CO2 in that situation? Absolutely yes. Adding CO2 to your aquarium becomes essential, and you’ll really need to invest in a CO2 system. That’s why I’m happy to share some practical tips for choosing a good CO2 system below.

Tips for a good aquarium CO2 system

As mentioned earlier, a CO2 system is quite an expensive investment, but in my opinion it’s also the most important one for a planted aquarium. A good CO2 system will usually last your entire aquarium-keeping career. For that reason, don’t go for the cheapest option — invest in the right, high-quality components. Not only will your plants be healthier, but you’ll also have a CO2 setup that keeps your tank running smoothly and looking great for many years.

What should you pay attention to?

• Buy a good needle valve that allows you to precisely control how much CO2 you inject — personally, I think this is the most important part!

• Pay close attention to the pressure regulator itself: avoid cheap metal and choose something solid that can handle enough working pressure without internal leaks

• Consider adding a bubble counter to your CO2 setup; these are available in both plastic and glass

• Invest in a solenoid valve to prevent waste and avoid gassing your fish at night.

By the way, I’ve already written an in-depth article about CO2 systems specifically for small or large aquariums. Definitely worth a read 🙂

How to mix CO2 into your aquarium

Once you’ve chosen your CO2 system, the only thing left is deciding which device you’ll use to dissolve the CO2 into the aquarium water:

• A CO2 diffuser: made of glass, works well, has a nice design, but requires more maintenance. Be sure to check my guide on CO2 diffusers;
• A CO2 atomizer: produces even finer CO2 bubbles than a diffuser and connects to your external filter (see the photo below);
• A CO2 reactor: delivers 100% dissolved CO2, but it can slow down your filter.

Conclusion: Does my fish tank need CO2?

You can absolutely keep an aquarium without CO2, but if you want fast plant growth or plan to keep demanding plants, I strongly recommend choosing a CO2 kit. In that case, don’t go for the cheapest CO2 system — invest in better quality. A good CO2 system will last your entire aquarium-keeping career and plays a major role in the health of your plants.

If you don’t do this, you won’t achieve the results you’re aiming for and you’ll probably end up realizing that spending a little extra would have been the better choice. In other words: wasted money. Be sure to also read the article where I explain the different CO2 systems for aquariums in detail.