The PoolRx+ booster contains the additional granular needed to replace minerals that are lost through back wash, splash out and algae kill. PoolRx+ booster can also be used for larger pools that need additional minerals when initially installing a PoolRx+ pool unit. The booster must be used with your previously purchased PoolRx+ pool unit. The granular does not need to go back into the PoolRx+ pool unit; it just needs to dissolve back into the pool water. The granular generally needs to be replaced every 4-6 months, depending on your swim conditions.