Use CO2 in your garden to increase plant yield by up to 20%. Plants benefit most from CO2 when the PPM (parts per million) of CO2 in the air is between 1000 and 1500. Ambient is is usually about 300 PPM. Use our CO2 Calculator for Grow Rooms to find out where to set the flow gauge on your CO2 Regulator, and how often to turn your regulator on. New to CO2 enrichment? Read our CO2 Buyers Guide and 'How To.'