The post-filter attaches to the Aquasana Whole House filter system, after the filter tanks, and removes particulates 60 times smaller than the eye can see.This includes insoluble minerals and cysts.The addition of this post- filter is considered a polishing agent and adds a level of protection for your household in the event of an outbreak of cryptosporidium or giardia.This cartridge should be replaced every nine to twelve months.