Sand cleaning

[rynoe]

After spending the last four months reading what seems like every post on this web site I am finally getting my tank on sunday. I bought a established 72 gal bowfront with some soft corals and a couple of clown fish. I was down at ocean aquatics and they suggested I replace the sand. Others have said to just clean the old stuff and re use. What should I do. If I do clean it do I just use fresh water?