Carbon Dioxide is one of the most important factors in an indoor growroom or glass house. Photosynthesis is the term used to describe the process by which plants combine CO 2 molecules with water molecules to form complex sugars, there is a resultant spare oxygen atom which is released back into the air, the sugars being further processed by the plant to form natural polymers for growth. The ambient level of CO 2 in air is 300-400ppm, fast growing plants in your growroom or glasshouse can use all the available CO 2 in less than an hour slowing photosynthesis and therefore growth to a virtual halt.