How to add C02 in small tanks

Setting up a small tank is trickier than it looks and getting the plants to grow can also be difficult.

You only have a small amount of water and aquatic soil to work with and as a beginner it can be frustrating seeing your plants not growing.

There is however a really simple solution to getting your plants thriving – pressurised C02 (carbon dioxide – which plants turn to oxygen and then grow, grow, grow!)

How to add C02 to a nano aquarium

For this guide I’ll be adding C02 to my Fluval Flex tank that was planted out in my setting up a planted aquarium guide.

For this you’ll need to have your tank setup and the following items.

Tropica co2 kit for nano tanks


Setting up the CO2 mini kit

In the box you’ll find the following items – 1 c02 cartridge, tube, holder and a hideous plastic canister for in your tank (you can swap this for a ceramic diffuser if you prefer).

The setup of this system is really easy and the instructions are clear.

  1. Pierce the C02 tank with the nozzle provided, just make sure the valve is closed before you do so. This can be a little tight but you’ll feel it when it goes through.
  2. Take the screw part off and then add the tubing over the tank nozzle, then screw over securing the tube in place.
  3. Place the other end of the tube over the end of the canister where the nozzle sticks out and place in the tank. Tip – fill the canister with water as you put it in.
  4. Slowly (and we mean really slowly) open the nozzle to let the C02 escape – the slower the better! Allow both sections of the canisters to fill with air.
  5. The C02 will now slowly diffuse out of the canister and into the water, you’ll then need to top it back up around twice a day – when the light is going to be on for a while.

Alternatively you can get a ceramic diffuser and just let it run, this looks better but means the C02 needs to be turned off and on with the lights.

Here’s how the setup looks:

C02 canister in a small tropical fish tank

When the canister needs refilling it looks like the below image – It always has a small air lock in the top.

Fluval 20g mini co2 canister when empty

And when full it looks like this:

Canister full of air

Fluval mini 20G C02 review
  • Ease of setup
  • Helping plants grow
  • Looks

Here’s a video guide of me filling the canister in a Fluval Spec tank 

Fluval pressurised C02 comes in larger sizes for bigger aquariums and I personally use the 88G model with a ceramic diffuser in my 190 litre Jewel Trigon corner tank.

5 thoughts on “How to add C02 in small tanks”

  1. Hi,

    Super useful info on your site, really liking it, wish you would write more 🙂

    Anyways, I’ve got the same Flex setup with the M50 heater and am trying to grow dwarf sagittaria, crypt parva and christmas moss that I’ve glued on manzanita wood to create a tree. How big of an impact would adding CO2 to this setup make?

    I’ve had it running for 3 weeks now (no fish) and am going through the new plant melting period and have some small new growth so far, was thinking of adding CO2 to help with their growth but wasn’t sure it would help that much. Thanks!

      • Thanks, that tank is looking great! I’d 100% recommend adding some c02 to get the plants established – if you us the product recommended on this page then you’ll just need 1 fill of it a day and that will get them growing.

        Am I okay to add your pictures to my Fluval Flex review page? I’d like to have a slider of “readers tanks”.

        • Certainly, you can add the pictures. I’m about to pull the trigger on the CO2, but have one more question. How does this kit work with the Flex cover? Do I need to have the cover off to have it connected?

          • If you send the tube in through the back where the wires go and then take it to the opposite chamber to the filter, push it through the grill and then attach the chamber to it and suction it to the side of the tank. The lid will stay on but just rest on the tube at the back.

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