I have used NSW and had no probs... I even say my colors were better when I used it.. When I use IO as a water change My tank goes throughbigger changes and even RTN on some corals,, but I only do water changes 2 or 3 times a year... If you have a small system I would diatom it first, not that that would make a difference though.. I pick up from a dock I use to launch my boat at during the incoming tide... But then again I'm crazy, I use methanol to cycle nitrates down to 0,,,,lmao.... Never had a nitrate problem in 4 years now though...lol...
I had the most probs when I do asw changes,,,,(ie algae outbreak, rtn, and Paying for salt),,,,lmao...