This Spa Frog® Filter Frog offers another approach to mineral spa care that fits in your filter. The unique design draws water in through the openings in the cap and the scooped louvers at the top and circulates it through the 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® Filter Frog lasts 4 months, with an easy reminder dial to help you remember when to replace it.