Do Aquarium Plants Need CO2? (Yes And No, Here’s Why…)

Image of aquarium plants breathing CO2

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Real aquarium plants are beautiful. They change over time, giving you something different to look at as they grow. They make your aquarium more alive and interesting, but they require more attention than artificial plants. So, do aquarium plants need CO2 (carbon dioxide) in the water to grow properly?

Yes, aquarium plants need CO2 to survive. However, there is no need to explicitly add CO2 to the aquarium water. Usually, aquarium water will have around 10 to 25 parts per million of CO2. This means the natural amount of carbon dioxide in the aquarium is enough to sustain the plant life within.

With that said, some plants can benefit from higher CO2 levels; it will make them grow faster and bigger. Something that should be noted when adding carbon dioxide to your water is that you must continue to add it to the tank indefinitely to sustain the plants. If you add CO2 to your water for a few weeks or months and then stop, your plants will suffer and probably die because they’re used to the higher levels. So if you’re going to add CO2 to get plant growth, don’t just do it for a certain time and then stop. The plants won’t survive with less CO2 once they’ve grown to a large size with the help of additional CO2. Before we go into further detail, it’s important to note that if you add too much carbon dioxide to your aquarium, you could harm or kill your fish. Get a CO2 meter as suggested further below to avoid harming your fish.

Do All Aquarium Plants Require CO2?

Yes, all aquarium plants require CO2, but there’ll always be a certain amount of CO2 in the water already without you adding any.

In fact, there’ll normally be enough CO2 absorbed from the air at the surface of the water. It’s produced by bacteria in the aquarium and by the fish that are in the water as they breathe. Plants even produce carbon dioxide when there’s no light shining on them, like during the night.

If you want your plants to grow faster, you can add CO2 to the water, but they don’t require extra CO2 to survive. Just know that if you start adding carbon dioxide to your water, you must continue to do so for your plants to stay healthy. You can’t just do it once for a boost of growth.

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Aquarium Plants That Do Not Need CO2

We don’t know of any plants that don’t require any CO2 at all. However, there are some plants that require less than others. For example, the Anubias species requires very little CO2 to survive. Other aquarium plants that don’t require much CO2 are Java Fern, Java Moss, Water Wisteria, Dwarf Sagittaria, Vallisneria species, and Sword plants.

If you plan to keep your aquarium lights on for over 12 hours a day, try to go for these plants because the longer you leave the lights on, the less CO2 there will be in the tank. This is because these plants absorb CO2 during the day and release oxygen.

If you like to keep your aquarium lights on most of the time, the plants will need more CO2 to keep up with the fast growth rate attributed to the lighting. So this means that in most cases if your aquarium lights are off for at least 10 hours a day, you can get away with not adding any additional CO2 to the water.

How Much CO2 Do Aquarium Plants Need?

Aquarium plants need around 15 to 30 parts of CO2 per million parts of water. It sounds like a minute amount, but it’s essential for the plants to survive.

The CO2 produced by bacteria and fish, together with the CO2 absorption at the surface of the water, is usually enough to keep your plants alive. Some plants may grow slowly, while others grow fast.

Some plants may look like they’re not growing at all if you’re not adding any extra CO2 to the water. This is not a problem as long as they look healthy. Most people don’t want the plants to take over the tank and therefore don’t add any extra CO2.

Signs Of Too Much CO2 In Aquarium

Given below are a few signs that show an excessive amount of CO2 in the water:

  • Your fish seem lethargic.
  • Fish gasping for air in the water.
  • The fish hang around the surface of the water.
  • Fish lose balance and coordination and plunge to the bottom of the tank, it’s a serious sign of CO2 deprivation.
  • Fish have a poor appetite.

The best way to determine if you have too much CO2 in your tank is to use a CO2 meter like this one on Amazon. This kit comes with a drop checker, suction cup, and 60 ml bottle of solution. After adding the solution to the drop checker, stick the drop checker inside your tank and wait for two hours to check the color of the solution. If the color remains blue, there is not enough CO2 in the water. If it changes to yellow, there’s too much CO2. And if the solution goes green, you have an adequate amount of CO2.

NilocG Aquatics Glass Co2 Drop Checker

Related Further Reading:

How To Reduce CO2 Levels In Your Aquarium?

If there is too much CO2 in your water, a large water change is the best way to remove it quickly.

Replace at least 70% of the water with fresh dechlorinated water and make sure it’s the same temperature as the water being removed.

How To Add CO2 To Aquarium?

You can add CO2 to your aquarium with a CO2 kit like this one on Amazon. There are many types of CO2 kits available, so select the right one for your tank size.

Fluval Mini Pressurized CO2 Kit

You can also make your own CO2 system with some plastic bottles, regulator, solenoid valve, needle metering valve, bubble counter, CO2 tubing, check valve, and diffuser. Add citric acid and baking soda to generate CO2 for a bit cheaper than buying the system and CO2 canister.

For most people though, buying the kit will be the better way to go, as you might not have the spare time and patience to build one up yourself.

Do Fish Produce Enough CO2 For Plants?

Fish alone don’t provide enough CO2 for plants to thrive. However, this doesn’t mean that you have to add CO2 to your water.

CO2 is also absorbed from the atmosphere at the water’s surface, and plants generate CO2 when the lights are off at night. Bacteria in the water also helps provide CO2 for the water.

All these instances of naturally occurring CO2 in your aquarium will suffice, and for the overwhelming majority of aquariums, additional CO2 is not required.

Interesting Further Reading:

Things To Remember…

Aquarium plants need CO2 for survival, just like any other plant. The good news is that there’s normally always enough CO2 for the plants to live healthily without you adding any extra. Your aquarium will get enough CO2 from the water’s surface, bacteria, and from fish breathing. Plants also release CO2 at night when it’s dark as they consume oxygen, so switch the lights off for at least 8 to 10 hours a day to get this boost of CO2 in the water.

If you’re looking for increased plant growth, adding carbon dioxide will work. Just don’t add too much, or you could gas out your fish, and they could die. If you plan on adding CO2 to the water, get yourself a CO2 meter as referenced above to make sure you’re not adding too much.

The less light you give your aquarium, the less CO2 you’ll need. So if you only switch your aquarium lights on at night for around 6 hours a day, you probably won’t need to add CO2 unless your tank is packed heavily with plants.