When to add co2???

I was wondering when should you add co2? I have 1 week old seedlings that are showing their first set of leaves and I'm not sure if i should add co2 and if so at what ppm level. They're currently in a humidity dome doing fine but if I can encourage better overall growth by starting early I would the know how. Thanks in advance!!!

I was told that CO2 is most beneficial during flowering. My homemade CO2 generator sits right under the ceiling in my flower room. Remember, CO2 is heavier than air. So string it up high so the gas can cascade down on your crop. BigSteve.

Bigsteve is correct....While you CAN use C02 in veg. The cost to benefit ratio is to low to make a worthwhile difference.

Start gassing at the onset of bloom. Be SURE to STOP gassing at the LAST 2 weeks before wash! The reason being that C02 will reduce the production of ethylene gas from the plant, and that helps maturation of the buds!