The problem could be a high bathing load (high pool usage) the solution may be as simple as a shock treatment.
It could be the start of algae growth. The solution to that would be to do a super-chlorination of your pool.
Incorrect water balance could also be the cause of cloudiness. If this is the case, check and adjust your chemical levels.
Poor filtration is another cause of cloudy pools. To rectify this simply clean or repair your filter and baskets.