i am a HnS user. Well take out your NW and check if there is snails or whatever items or sand bits stuck @ the nw. take it out and ofccoz run in inside in your or a pail of water to check for the performance. well need lots of "fine tunning"
ytd i just found out my hns not working and true enuff there is a snail shell @ the nw. so i remove it and the nw become very noisy so after cleaning and cleaning its back to normal
i just finished installing my hns Nw pump into the skimmer. still under observation.