WASH the sand. It may take a swimming pool worth of water---at least it seems like it. THis is best done in the back yard with a hose, and a small amount of sand at a time. Use Prime to remove chlorine from city water, and drain well. White powdery gunk does not belong in your tank. [Honestly, most of us add sand just after base rock, then live rock, but if you wash it really, really well, you can do this ok. Even so, expect some cloudiness until bacteria has had time to coat the remaining fine particulate.]