[DiverDude]

I would use RO/DI water but some people get away with tap water and prime (depending on your local water).

One thing I learnt fast is to forget about pouring water into a reef tank unless it's a small quantity. Even in my little tank, I do 5 gals at a time and it's to heavy and you have to pur too slowly to avoid stirring up all the sand.

I siphon the water out and pump in the new water after it's circulated for at least a day in a bucket.