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