Filter Cartridge replacement. Schematics 65 square feet of surface area 8 1/2" Outside Diameter x 10-1/4" Height x 3" Inside Diameter Remove the filter lid. Remove any debris from the filter compartment. Unscrew the filter retainer (located on the top of the filter standpipe). Caution: Do not remove the filter standpipe while removing the retainer. If the standpipe inadvertently get unscrewed while removing the filter cap, immediately separate the two components and reinstall the standpipe. The spa must never be operated without the standpipe in place. Remove the filter. To reinstall the filter, reverse steps 1 to 4. Caution: Do not over-tighten filter retainer! Over tightening of the filter retainer will result in removal of the filter standpipe during the next filter removal.