Have any of us used Seachem's Purigen? Is this stuff any good? I have a 75 gal mixed tank with 15 gal sump? My sump has a sock at the drain with protein skimmer at one end , with a middle resorvoir for return and a 3 gal refugium at the other end. ( By the way, I clean my sock on a regular basis)If you have used this Purigen, where do I place this stuff in the sump? Hopeing it will reduce nitrates. All other chem parameters are good. Thanks to all, Ron.