Build your CO2 system
How big is your aquarium?
We use this to choose the right size of diffuser for you.
Not sure? Measure your aquarium in centimetres, multiply length by width by height, then divide by 1,000.
Where are you?
CO2 bottles have a different thread in different parts of the world. Tell us where you are and we build the regulator with the right one.
Which countries?
Every country in Europe, including the United Kingdom and Ireland. Australia and New Zealand. And most other countries outside North America. If your bottle has its thread stamped on the neck, the stamp wins: W21.8, DIN477 or BS341 is this one.
Which countries?
The United States and Canada. If you live somewhere else but your bottle came from North America, choose this one. A stamp of CGA320 on the bottle's neck is the sure sign.
Not sure? Look at the neck of the bottle, or ask the shop that fills it. Every CO2 bottle sold for aquariums, beer or fire extinguishers uses one of these two threads.
What filter do you have?
This decides how the CO2 gets into your water.
Anything else, and the CO2 goes in through a small diffuser inside the aquarium
Not sure? Look under your aquarium. If there is a box with two hoses running to it, that is a canister filter.
Choose your regulator
It sits on the bottle and sets how much CO2 goes into the water.
How many aquariums will it feed?
Manifold block€47.99 each
Bolts onto the Pro-Elite and adds an outlet. One per extra aquarium.
2 aquariums
we add 1 manifoldmanifolds, €47.99
Both regulators come with a bubble counter, so you can watch the CO2 going in. The Pro-SE is right for one planted aquarium up to about 250 litres.
How should the CO2 go into the water?
With a canister filter most people take the inline diffuser, which goes into the filter's hose. The other two sit inside the aquarium.
With a sump, or no filter yet, you can take the inline diffuser — it sits in any hose with water flowing through it — or one of the two that sit inside the aquarium.
Both of these sit inside the aquarium and make a fine mist of bubbles.
Put it low in the aquarium, as far from the filter's outlet as you can.
The hose size is printed along the hose. An in-tank diffuser works with a canister too.
How far is the bottle from your aquarium?
This is the tubing that carries the CO2 from the bottle to your aquarium.
Measure to the top of your aquarium, then add half a metre for the bends.
The last few things
We have ticked what most people take. Untick anything you already have.
Your system
One part. parts. Tap any line to change it.
You pay for the parts, nothing more. There is no extra charge for buying them together.
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What you have chosen
Nothing yet. Every answer adds a line here.
Four systems we put together ourselves. They cost the same as their parts, so a kit is a shortcut, not a different deal.
A kit opens with its parts and their sizes — choose what fits your cylinder and your aquarium, then add it. It does not fill in the seven questions.