GE Osmonics MERLIN-3038333 Merlin RO Carbon Pre Filter Advanced fibredyne technology provides 3 times the holding capacity of a standard carbon block filter Reduces chlorine and sediment to protect the membrane from fouling for up to 10,000 gallons of use Only one pre-filter is needed per Merlin system For well water systems you can use the Merlin 1266690 sediment-only pre-filter