Notice a difference? No, not really but it is hard for me to tell because I started my reef with all NSW and there always has been some NSW in there. I don't know how long my tank would have lasted with all ASW. Maybe there is no difference. But I try very hard to keep my tank as natural as I can which is why I have no reactors, dosers, controllers or anything else except perhaps a Supermodel to come over occasionally to tell me how good it looks.
I use mud and amphipods from the sea so I would imagine for my tank, NSW is not that important. But NSW has every chemical on earth in it including Amelia Airheart's socks and Jimma Hoffa's ear wax. No one knows if any of that stuff or other stuff like Kriptonite, Un-obtainium, or any of the thousands of other minerals is of a benefit or a detriment in a marine tank. ASW contains what we think our animals need in the proportions of what we think they need but no one really knows. We do know that it will keep our tanks going and healthy but I would have to doubt it is "better" than NSW. If you can get NSW, and it is free for the taking, why not use it?
That noncence about introducing diseases and paracites is rediculous but if you are worried about that you can diatom filter it, add bleach, heat it a little, like to 98 degrees for a day or keep it with no animals for a few weeks. I myself just wait till it warms up and dump it in. But I am not a Sissy or Girly Man. :plane: