need more info to help;
how long has your tank been up?
is the cloudiness a recent thing or has it always been like that?
what kind of sand are you using?
have you changed anything recently that coincides with when the cloudiness started?
what are you adding to your tank (food/suppliments/calc reactor)
what are you using to polish your water (carbon, gfo, pellets)
what's your salinity at and how are you measuring it?
what's your maintenance schedule and process (water changes, filter changes, etc.) - are you using RO/DI with 0 TDS for water changes?
are you running a sump? do you have a filter sock/floss?
pictures help as well