Pentair FNS Plus DE Filter w/o valve 36 Sq Ft »» Description : Pentair FNS Plus DE Filter w/o valve 36 Sq Ft Filtering with the Pentair FNS Plus DE Filter with diatomaceous earth (D.E.) gives you water that really sparkles. Thats because D.E. filters remove the tiniest of contaminantsparticles as small as 5 microns. (An average grain of sand is 1000 microns!) Even though these particles cant be seen individually, collectively they greatly affect water clarity.