... 2.Carbon layer thick: 35mm,50mm High Efficient Active Carbon Air Filter *Carbon layer thickness: 35mm, 50mm*Color available: Black, ... are constructed with a 'packed bed' design to give consistent performance, long life (12 to 18 months), and are completely ... , including Grow tent ,hydroponics,greenhouse air cleaning.etc.And we suggest you apply air filter together with ventilation fans 4. Specific ...