There's no co2 absorbtion at night because when it's dark, there's no photosynthesis going on so no need for co2...

Photosynthesis occur only when the plant receive light and convert co2 into o2.

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mafia819 Reviewed by mafia819 on . using dry ice 4 co2 ive got 2 shop lights with 2 builbs in each light, 60 watts each builb, and 4 plants inthe center of the lights. i keep the lights about 2 inches from the top of the plant. the lights are hanging from the clothes rack in my closet. i bought a little fan and some plastic drop clothes (the ones for panting). covered the whole thing with the drop clothes so its hanging from the clothes rack to the floor, got 3 pounds of dry ice put it in a tub with warm water and stuck it in the enclosed area on Rating: 5