... 3.Carbon layer thickness:35mm,50mm Hydroponics Active Carbon Air Filter for Green House *Carbon layer thickness: 35mm, 50mm ... which can allow untreated air through the system. And Housing Material is Galvanised steel & high impact polycarbonate cap. 3 ... the Greenhouse systems: Inline ventilation fan, Grow tent, Carbon filter, Light reflector, Electronic Ballast, Heavy duty hanger, Flexible duct ...