what color is the cloudy water? if its green/red its diatoms. If its white/grey it could be sand suspended. It will calm down on its own if its sand. If its diatoms, water changes, increased filtration and beefing up your CUC can take care of it. If thats not possible, do water changes, it'll disapate on its own.
If you are just setting up a new tank, the sand can release dust into the water, which clouds it. When cloudy water becomes an issue, i've used a couple tricks. A power filter with floss/carbon can take care of it quickly. Canistar filters will too. If those arent an option, take a pair of pany hose, cut off 4-5 inches of the end, fill that with synthetic pillow stuffing, and tie that over your returns for a couple days. THat trick works well and setup cost is less than 3 bucks.