It’s always been advised to wash sand thoroughly prior to putting into your aquarium. While it may knock down on some of that initial cloudiness, it has been my experience that it really doesn’t matter if you wash sand or not. The cloudiness is meaningless for a new aquarium. You’re not putting in any livestock anyways. Instead, you’ve got a month or so before your tank will even be remotely ready to receive fish or corals, and adding live rock will only cloud up the water anyways, so why waste the time and effort on the sand? To further make the step pointless is the fact that once you fire up the skimmer, canister filter, filter socks, and the rest of the filtration system, most of that cloudiness will vanish on its own anyways.