One side of the carbon filter is coated with Ti02 (titanium dioxide) to increase the photocatalytic power of Hextio. This side is a pale silver grey and should be placed face down. The black side therefore should be positioned so that it faces upwards.
Replace at least every 6 months. In the meantime it is a good idea to check the carbon filter once a month and clean it gently using a vacuum cleaner. Simply unscrew the two screws on top of the grill to remove and replace the filter.
Always switch off and unplug the unit prior to any maintenance and NEVER look directly at a burning UV light.