Swimming pool owners need to shock their pools occasionally, especially when algae or other debris contaminates the water. While shocking normally leads to clear, clean water, sometimes the water will turn cloudy or milky. The higher levels of chlorine that result from shocking aren't to blame; rather, it is the dead matter that is sometimes left behind.
Causes of Cloudiness
Since pools are susceptible to algae growth when their chlorine levels drop, it is recommended that pool owners shock the water at least once a week to keep an appropriate level of chlorine in the water. Shock should also be added at the first sign that algae is developing in the water. When you shock the water, it can leave dead matter behind. This dead matter can leave behind a cloudy residue.
When you shock your pool and it turns cloudy, it is often the result of a build up of dead or dying algae on the surface of the water. This is also known as biofilm, according to Par Pool & Spa. To kill off the biofilm, add an additional amount of chlorine or shock based on the instructions on the back of the container. After this additional chlorine, the water should begin to clear up. Pool owners can also add a clarifier to the water after the additional chlorine to help bind the biofilm and other matter for easier filtering.
When you shock the water in your pool, sometimes the water can turn a milky white. Milky white water happens when the water is shocked using a calcium hypochlorite based chlorine and the water in the pool already has a high concentration of calcium in it. High levels of calcium in the water indicate that the water is too hard. If the calcium level is above 200 ppm and you are adding a calcium hypochlorite based chlorine, then milky water is often the result.
In order to prevent milky or cloudy water in the pool, it is best to maintain a consistent level of chlorine and pH. Chlorine levels should stay between 1 and 3 ppm, while the pH needs to stay between 7.2 and 7.8. You can use a calcium sequestering additive in the pool to remove the milky white water or you can use a sodium hypochlorite based chlorine instead of a calcium hypochlorite based chlorine.