Skip to Content

How To Set Up a Basic CO2 System in a Planted Tank (Guide)

get 5 secrets to thriving plants

I remember how scared I was to make the big jump to a CO2 system for my planted tanks. It really feels like a daunting and difficult leap, but over the years I’ve learned that it’s not that difficult at all. Here’s why.

To set up a CO2 system in a planted tank, purchase all the essential components. Connect all components accordingly. Open the needle valve of the regulator to allow CO2 to escape. Start low and slowly increase the amount of CO2 to the optimal dosage. Use a timer to only inject CO2 during daytime.

Don’t leave just yet, because I’ll be sure to explain all the components so you know what they are. I’ll also guide you through setting up a CO2 system in more detail. After reading this page, you’ll know exactly what to do and even more important: what not to do.

Setting up a CO2 system step by step

A little bit further down the article I’ll explain all the different components of a CO2 system. Because you’re probably looking on how to set them up in your tank, I’ll cover that first. All information is present on this page, so let’s dive straight in.

1. Attach the solenoid valve to the regulator. I put this as step one because I like to prepare my regulator before screwing it on the bottle. As a recap: the solenoid valve is the thing you plug in the power outlet and controls if CO2 can come out of the output of the regulator.

2. Screw the regulator on the CO2 bottle. Make sure that the needle valve on the regulator is turned to the closed position. Screw the regulator to the bottle.

3. Fill up and connect the bubble counter. There are different types of bubble counters, some of which are integrated in the diffuser. If yours is not, this is the time to fill it up with a little bit of water and attach it to the output of the solenoid valve. Some screw straight on the solenoid valve, others require a little bit of tubing. Tip: make sure the bubble counter is as close to the regulator as possible. You’re going to use it to measure how much CO2 you’re injecting. If there’s less tubing between the diffuser and the bubble counter, there’s less delay.

4. Add a long piece of tube to your diffuser and stick it inside your aquarium. The tube should be long enough to bridge the distance between the regulator on the bottle and the diffuser in your tank. If your diffuser releases tiny bubbles that than dissolve in the aquarium water, try sticking it to the glass as low as possible. This gives the bubbles as long as possible to fully dissolve.

5. Add a check valve to your system. A check valve or return valve makes sure that the tube reaching into your tank is one-way traffic. Some diffusers have a built-in check valve, but if yours does not you’ve got to buy a separate one and install it between the regulator and the diffuser. Just take a pair of scissors, cut the tube and put in the tiny return valve. Try to install the check valve as close to the water level as possible (not in the water). It prevents accidentally starting a siphon and draining your tank.

6. Connect the tube leading from the diffuser to the output of the solenoid valve. You’re almost ready to start injecting CO2.

7. Fill your drop checker with fluid and stick it to the inside of your tank. The color of the drop checker will indicate whether you’re adding enough CO2. It does not really matter where you put it, as long as you don’t stick it close to where the CO2 is added to your tank as that might give a wrong reading.

8. Plug your solenoid valve in a power socket. Make sure to use a timer, because you only want to release CO2 during daytime. At night, it’s dangerous to inject CO2 because your plants are not processing it. If you inject CO2 at night you risk gassing your fish which will potentially kill them.

A few things to add:

  • A diffuser needs a few days before it starts to work properly. When it’s brand new it’s not able to release tiny bubbles. This is normal, give it some time.
  • Turn on your CO2 about 2 hours before the lights turns on
  • Turn off your CO2 about an hour before the light turns off

How much CO2 should you inject in your aquarium?

The amount of CO2 that you add to a tank is measured in bubbles per second. That’s also where the bubble counter comes in. The amount of bubbles per second for each tank is different. Some aspects that affect this are tank size, quality of your diffusor, amount of plants, amount of surface agitation and even the KH of your tank. Because of this, nobody can give you the correct amount of bubbles per second!

Of course you need to start somewhere, and this is something I understand. When I first started out a friend of mine recommended starting with approximately 1 bubble every 2 second. This is equal to 15 bubbles in 30 second. It can be really annoying to set the correct amount because of the delay between turning the valve and seeing an increase in bubbles. Also, turning the needle valve on the regulator just a tiny bit gives a pretty large change. You’ve got to fiddle around with this a little bit.

You’ve got to start adding just a little bit of CO2 and slowly increase this amount over time. Make sure to have your drop checker installed! You’re going to use this a lot the first weeks. Try aiming for a green drop checker and you’ll be fine.

Another great indicator if you’re adding enough CO2 (and not too much) is measuring the pH of your tank. More dissolved CO2 lowers the pH, so if you know the pH you can say something about the amount of CO2. Try aiming for a pH that remains above 6.5. Adding more CO2 can suffocate your fish.

All components that you need to set up a CO2 system for your aquarium

There are many different brands on the market, and in my opinion the brand is not that important. The only component I recommend buying from a reputable brand is the regulator, because it’s important. Below is a list of all components that you need, what they do and why you need them.

  • CO2 Cylinder: contains your CO2. You can buy these at your local fish store, but you can also use a CO2 fire extinguisher. That’s what I do. If you can get your hands on expired CO2 extinguishers this can be a cheap source of CO2.
  • Regulator: this is what controls the amount of CO2 that you release from the bottle. It’s an important component that needs to be of good quality because it deals with high pressure. It also needs to be accurate and consistent. It has an indicator that shows how much CO2 is left in the bottle.
  • Solenoid valve: the solenoid valve turns the flow of CO2 on or off. If it’s plugged in and has power, it releases CO2. If it’s not powered no gas can flow through. This is an important part of your setup because you can now use a timer to turn the CO2 off at night.
  • Bubble counter: a good indicator of the amount of CO2 you’re adding to your tank. There are different types of bubble counters. Not much more to say about it.
  • Check valve: prevents water from flowing back into the CO2 tube. It’s very cheap and essential because otherwise you risk starting a siphon and slowly draining your tank at night. Don’t skip out on it.
  • Diffuser: the part where the gas enters your aquarium water. Common diffusers break up the CO2 into tiny bubbles and releases it in your tank. You can also get really large plastic ones that take up a lot of space. Another option is in-line diffusion which allows you to dissolve the CO2 into the outgoing water flow of your canister filter.

Great job! You’ll definitely see the benefits of additional CO2. Although there are plants that can do great without additional CO2, like these ones, every single plant benefits from more available dissolved CO2 in an aquarium.

get 5 secrets to thriving plants