I have used it for water changes ,and my SPS corals love it. I collect on an incoming tide just before high tide. I pump from about 6 feet down. I haven't had problems with parasites at all. Red Tide would be a problem ,but I don't collect water when red tide is in the area. I change out approximately 80 gal. at a time. Ted BTW I'm also running 80 watts of UV.