Colombo Advanced CO2 Advance RegulatorColombo Advanced CO2 Advance Regulator Plants need CO2 for their growth. During the day, when there is light, plants absorb CO2 and produce oxygen. During the night this process reverses, CO2 is released and oxygen absorbed. Due to the fact that aquarium plants grow underwater, they need to absorb CO2 from the water. In normal conditions aquarium water does not contain sufficient amounts of CO2 for healthy growth. With a CO2 system, CO2 gas is added