This SPA FROG offers another approach to mineral spa care that fits in your filter. Our unique design draws water in through the openings in the cap and the scooped louvers at the top and circulates it through our mineral formula for greatest effectiveness. Water is then released through the bottom openings. Simply supplement with a low level of bromine or chlorine. This SPA FROG also lasts 4 months, with an easy reminder dial to help you remember when to replace it.