My process for my 2x2.5 grow tent is as follows. Passive air intake with a 4" exhaust fan for month 1, ducted out of tent. At 30 days I hook up a Cheapie very used HTG carbon filter to the 4" fan and duct out of tent. I begin flowering at this point, but don't need serious odor control. 4 weeks into flowering I switch to a new Phresh carbon filter ($80) for weeks 4-10. I also add a Ona bucket in the room outside my grow room for safe measure and residuals. I don't like the Ona even in the same room where its scent can be intaken into my grow area, let alone actually in my tent! I am very particular about anything that can change the taste and flavor.