I just got done adding Quickrete sand to my estbalished FOWLR tank. With a combonation of siphoning and scooping, I removed half (probably closer to 2/5) of my old crushed coral substrate. I tried adding the sand w/ the pipe method and that didn't go so well. It was slow, hard to control and made almost as much mess as scooping and slowly dumping at the bottom. The cloudiness is quickly subsiding.
Jason