First be careful with that many plants, when flowering starts neighbors may smell skunk. Also the main aspect to venting, or at least what I have read, is that plants need fresh air. You might try an ionizer. And lastly to remark on SlipSLide's comment, plants only use CO2 during day for the photosynthetic process. (CO2+Sunlight+H2O=gluecose, byproduct=O2). Thats just my amatuer input.