Usually within a week. Make sure you are running your pump 24/7 as Janet suggested. If, after a week, you are losing no more than 1 ppm of chlorine overnight and it is still cloudy, you might add a dose of Polyquat 60%. It is the only algaecide we recommend, (although algaecides are more of a preventative against algae forming rather than taking care of an algae problem) but it will also act as a clarifier which might help.

But -- give it a week. It will probably be cleared up in that time.