Filter Cartridge For Sundance Spas MicroClean I Filter System. The MicroCleancartridge provides maximum filtration for crystal-clear spa water. For use with Sundance 850 & 780 Series Spas. The complete MicroClean I Filter System pictured in insert is to help ensure you select the correct replacement filter. Each MicroClean I Filter System component is sold separately. Approximately 14 Inches in length by 8 1/2 inches in diameter and has a closed top with SAE threads and a 2 1/2 inch opening on the bottom