The Kronus 4® controls temperature, humidity and CO2 in your grow area at your preferred settings. The built in ten (10) minute'CO2 delay' feature deactivates CO2 equipment if the temperature setting is exceeded. The'CO2 ON' feature is only activated during daylight periods to dose CO2 when your plants are able to uptake it, and is disabled during the nighttime hours or when the temperature exceeds the preferred setting. The'Night Only' output allows use of a nightlight or circulation fan. The Kronus 4® gives the expert gardener the top shelf controller they're looking for to maintain their garden!