Been noodling on design of two grow tents. Decided on two tents 3ft wide four ft deep six ft high. Plan on one 90 watt UFO LED light per tent. For CO2 enrichment I plan to put a fermentation jug in each. For ventilation I plan on a tee shaped vent tube with filter box and fan at end of center leg of tee. Plan to control fan speed / cfm with a dimmer. The 64 thousand dollar question, how do I know how much air to exhaust without wrecking the passive co2 enrichment?