I have a prefilter as well but I keep having problems with the Nozzle and Venturi getting clogged. Once this happens the system can not draw the Potassium Permaganate into the resin bed. This is not covered by the warranty and is hard to detect by the casual user. I feel this is a main flaw because the nature of the water this filter is designed to clean cloggs the nozzle and venturi.It also seems that once clogged the venturi cloggs quicker and quicker causing the filter to fail.If there has been a redesign of this issue I would love to be informed.