CO2 System and Accessories
Everything for a planted tank CO2 system: regulators, diffusers, reactors, drop checkers, tubing and kits.
Advice and care
How to choose a CO2 system
A CO2 system is a cylinder, a regulator and a diffuser, each chosen to suit the tank.
Solenoid valve
A regulator with a solenoid switches CO2 off at night on a timer, when plants do not use it.
Diffuser by volume
A diffuser suits a small tank, a reactor on the external filter hose a larger one.
Drop checker
A drop checker's colour shows whether the CO2 level is right.
Popular brands
All brandsFrequently asked questions
Is CO2 dangerous for fish?
Too much is, so raise the amount slowly and watch the fish. If they gasp at the surface, reduce CO2 at once.
Which cylinder does a regulator need?
Check the regulator's thread, such as W21.8×14, and choose a matching cylinder or adapter. The thread is in the product name or description.
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Plants need carbon to grow, but aquarium water usually holds little of it, especially under strong light. Added CO2 speeds up growth, helps carpeting plants grow dense and gives red plants their colour. In a low-light tank with anubias and mosses, CO2 is usually not needed.
A system consists of a regulator, bubble counter, check valve, CO2-proof tubing and a diffuser or reactor. The check valve stops water from flowing back into the regulator. Ordinary silicone tubing lets the gas escape through its walls, so use CO2-proof tubing. Ready-made kits for smaller aquariums come with parts that already fit together.
Switch the CO2 on about an hour before the lights come on and off an hour before they go out. The most common mistake is raising the dose too quickly: increase the bubble rate gradually over several days and watch how the fish behave.
Related guides
All guides
CO25 min read5 sections
Sodastream cylinder adapter: thread and regulator
Sodastream cylinder adapters by the makers' data: the W21.8×14 thread, Quick Connect, working pressure, seals and the makers' safety steps.
Read the guide
CO22 min read5 sections
CO2 in the aquarium: do you need it and how to choose a system
When an aquarium needs added CO2, how cylinder and bio systems work, how to set the amount and check it with a drop checker.
Read the guide