LAVENDER works a treat i think its got something to do with the way smell works ,, you want something that gives off the same smell chemicals and i have found that lavender works a treat. i pass the air i am putting into my room through a cotton pillow case full of lavender , and the same on my outward bound air. so the air gets sucked in through lavender and then blown out through lavender,, this works for me but my grow is small and so is my room ... good luck pal