EHEIM CO2-SET Diffuser 400lCO² gas is atomized into many bubbles by the diffuser. The bubbles create a larger contact area and the CO² can dissolve quickly into the aquarium water. The bubble counter visually monitors the addition of CO2. As a rule, about 20 mg of CO2 per liter. This corresponds to about 10 bubbles per minute per 100 liters of water.