I own an HS Envoy with five filters. I bought just one extra filter to add to my rotation. That way, I can have one hanging out in my basement soaking in a bucket solution with TSP overnight, rinse etc and still be able to use my spa. Once a week I rotate my filters, pop the clean one on the gray standpipe, and then clean the next one. This works especially great in the Winter when I can't easily remove and clean all five filters.