I think u just want to open it fully once a day to get co2 o2 exchange. The plants breath in the co2 and exhale the o2. With the lid closed they don't get more co2 cause they use it all. Once a day should be fine at the end of your light cycle, but I may be wrong. Others chime in if I am. Yes, the plants do exhale co2 at night but I don't think enough.