What should I do before shocking a pool to clear cloudy water?

Test and balance the water chemistry first. pH should be 7.4–7.6, total alkalinity 80–120 ppm, and calcium hardness in range. Unbalanced water makes shock ineffective. Then shock, run the pump 24/7, clean the filter, and brush and vacuum. Patience is key—it takes time for the filter to clear the water.