Cloudy pool water indicates some sort of problem with one of your pool's systems, and that the quality of the water isn't as high as it should be. Thankfully, while there are a number of reasons why your pool water could be showing up cloudy, it is fairly straightforward to troubleshoot each of them so that you can restore your pool water to its clear and clean ideal state.
Pool Filter and Pump
Cloudy pool water is most commonly caused by a high concentration of algae, dirt, or some other contaminant or debris. This can occur suddenly if there is some sort of problem with your pool filter or your pool pump. Inspect your filter, and clean it if necessary to remove any debris that may be clogging the filter from properly filtering your water. For sand and diatomaceous earth filters, all you have to do is use a garden hose and the backwash setting on the filter to clean them out, though you will have to add more diatomaceous earth. For cartridge filters, you'll have to spray them down and apply a degreaser, or even purchase and install a new cartridge if it has reached the end of its lifespan. Additionally, check your pool pump for signs of damage: if it is leaking, operating improperly, or just otherwise appears to be on its last legs, you should contact a pool contractor immediately to take a look at it.
Use a Pool Clarifier
If your pump and filter are working properly, the issue may be the size of the particles in the water. You can treat this by applying a pool clarifier, which will cause the small particles to begin to clump together, creating larger bits that will be picked up by your filter over time through normal operation. After applying, you should see your pool water begin to clear up within a few days.
Check Chemical Levels
Check your pool's chemical levels to see if there is an imbalance in your chlorine levels or your pH. According to the CDC, you'll want to have a pH of 7.5 or so, and will have to add a pH minus or plus product to get your pool to the right level. Additionally, keep an eye on your chlorine levels: again, the CDC recommends a level between 1.0 and 3.0 ppm, so if your test strips say otherwise you may have to add more chlorine to your pool to kill the microbes and bacteria that are clouding the water.
For more information, contact companies like Pettis Pools & Patio.