To clear up cloudy blue pool water, check the pool filter, the pH balance and the oxidation of the water. Stir the water and skim the debris from the top and the drains. Use a weekly water clarifier. Add a pool flocculant to the water to solidify any particles forcing them to the bottom of the pool, and use a pool vacuum to remove the particles.
Check the pool filter's operation to ensure it is working between eight and 10 hours a day. Check the filter for clogs. Backwash the filter regularly by reversing the water flow occasionally to flush it. Use pH test strips to ensure that the pH is between 7.2 and 7.6 with an alkalinity between 80 and 125 parts per million. If you are regularly adding appropriate chemicals to the pool but there is still cloudiness, shock the water to oxidize it.
To use a pool flocculant, change the pump to a recirculation setting to keep particles from getting caught into the filter. Add the flocculant to a bucket of water, following the manufacturer's instructions. Pour it into the pool and let it circulate through the pool for several hours. Allow the particles to settle at the bottom by turning off the pump for a few days. Vacuum the particles after setting the pump to a waste setting, leaving a hose running in the pool during the process.