Another popular method of generating DIY CO2 is to use a citric acid  and baking soda .

The pressure in the bottles will want to form an equilibrium because they are connected by tubing. So when the pressure is higher in bottle A than in bottle B gas will want to flow from A to B. A consequence of this is that citric acid is injected into bottle B when the pressure in bottle A becomes higher than that in bottle B, which in turn creates more CO2. This additional gas is pushed into bottle A (as well as your diffuser), again making an equilibrium but in reverse to before. When the pressure in B falls below A, citric acid is again pushed from A to B, and so the cycle continues. It’s an ingenious system!

INSTRUCTIONS FOR DIY CO2 USING BAKING SODA AND CITRIC ACID

2 x 2L Plastic Bottles, e.g. Coke or Sprite.

Bottle A
200g Citric Acid Powder.
Mix with 600ml Water until dissolved.

Bottle B
200g Baking Soda
Mix with 200ml Water until dissolved.

To start, citric acid or vinegar is poured into bottle A, and a mixture of baking soda and water is poured in bottle B. The caps with tubing attached are the screwed onto the bottles.

The needle valve is opened, and bottle A is squeezed slightly to inject Citric Acid in to bottle B. This starts the generating of CO2. The needle vale is then closed to allow pressure to build in the bottles.

Mix bottle B by swirling the mixture around – you should see some bubbling. If not, squeeze some more citric acid from bottle A.

When the pressure gauge reads 1.5 bar in bottle A you can slowly open the needle valve to begin the flow of CO2 to your diffuser.

DIY CO2 System Using Citric Acid / Baking Soda