Spa Frog Serene Mineral Cartridge by King Technology

For use in the Spa Frog Floating and In-Line Systems. Set Minerals to #6 (wide open). Lasts 4 months or until spa is drained and refilled. Simply discard and replace.
The SPA FROG In-Line System, with its patented design, is built right into the spa using the same replaceable mineral and bromine cartridges as the SPA FROG Floating System. Simply open the cap, pull up the holder and snap in the cartridges.