did you put crushed coral in the tank? did you rinse it off first?
i rinsed mine off quite alot and it still clouded up for almost a day and a half.
do you have anything living in it yet? if not, i have read on this board about turning off your pumps, filters, powerheads and letting it all silt down.
water changes may also do the trick.
i am pretty new to this, so i could be wrong.
unrinsed crushed coral + added directly to tank = giant silt storm.