Hi Dave, I have used NSW on reefs with no problems. I grew up in Winthrop, MA. In high school, while volunteering in husbandry at New England Aquarium and working at a pet shop (pet supply depot on route 1, Saugus... the first NE Petco after we were bought out) I started using NSW on my own tanks. Inner Boston Harbor water taken from sand filtered spigot used in every exhibit in the building that had seawater. After I got tired of lugging buckets in my car after a full day at the aquarium I just collected water on days after long dry spells at a local beach on calm days with incoming tide, near high water. I never filtered this water, just heated and used. Never noticed a problem with any creatures I kept. Over 16 years ago I collected NSW with a 12 volt bilge pump and cigarette lighter plug with extension cord that I filled garbage cans with in my pickup to drive home. Did not filter that, collected on a boat ramp like Paul B. Then, I had to move to Maine for work, the employer had a marine lab with flow through raw seawater that I used again taking Jerry cans home, no issues. More recently I started using water from Buzzards Bay collected along the shore of New Bedford, close to a sewer outfall and at the mouth of a Cove with CSO’s that still discharge in big rains. This comes into a seawater lab in my work building. I can take it for free. This water is filtered through some fancy filters and UV sterilized. No problems. Hanna ULR PO4 tests practically zero. Calcium no lower than IO. All kinds of life Corals Clams Fish Inverts no problems. I did not filter in my younger days and would not now either, it is just easy where I get it now... if your water is sediment laden you could filter it with a fine cartridge. I did use a canister for that but ended up realizing my feather dusters and all the sponges cleaned it faster and better anyway, and seemed to thrive too, while getting it. I encourage you to try. It never hurt my pets. Just heed the advice of collection on incoming tides, near high water, in the most seaward location you can after dry periods with little rain. I have been doing this for over 20 years. PaulB has me though!!!