... -1250mm 2.Carbon layer: 35mm,50mm 3.High effective 4"-12.5" Hydroponics Activated Carbon Ventilation Filter *Carbon layer thickness: 35mm, 50mm ... a 'packed bed' design to give consistent performance, long life (12 to 18 months), and are completely maintenance free. The packed ... , Heavy duty hanger, Flexible duct... Rope Ratchet Filter Hanger 4"-12.5" Hydroponics Activated Carbon Ventilation Filter