Cloudy pool water is a common occurrence in pools. This is caused by suspended particles that cannot be easily filtered out. There can be quite a few reasons why your pool water is cloudy. Some of the most common reasons include:

Chemical balance of water is off. If pH or chlorine levels are off then that could be a reason for cloudy water.
If the pH levels are too high it inhibits the action of chlorine. This results in low chlorine levels that promote algae growth which then causes cloudy water. Algae growth causes cloudy or green water.

This water problem can also be caused by low or inadequate pool sanitation or oxidation. Natural sunlight is an excellent natural oxidizer so make sure pool is exposed to adequate sunlight. Algaecide can be added to get rid of the algae.

When pool filtration system is not functioning properly then it will result in murky water.
If pool pump is not working properly then it can cause poor water circulation.
Contaminants from swimmers, such as suntan lotion, bacteria and cosmetics can make water cloudy.
As a first step, check the pool filtration system. Pool filters need to be cleaned or replaced regularly to eliminate any filtration problems. Run the filter and pump for 24 hours straight for a few days until water becomes clear. Improper maintenance, such as neglecting vacuuming and brushing, can lead to a dirty looking pool. Shocking the pool once a week or biweekly helps maintain chemical balance.