I replace this Sealand filter about once a year. Depending on where you go they are from $75- $125. After replacing my most recent one I decided to cut open the old one. Its a 2" piece of PVC. I found it filled with granulated charcoal and a round piece of screen on each end to keep the charcoal inside. See pictures. So I ordered a 4lb jug of activated charcoal from buyactivatedcharcoal.com. Went to HD and picked up a 2" Fernco coupling. Cleaned pvc and screens with hose and put new charcoal in pvc tube and used the Fernco coupling to put back together. Total cost. $4.00 coupling and 4lb box $35. The charcoal should last me for the next 5-10 yrs. Anyone else do this? All I can say is there are some huge margins with this component.