Once you have that new swimming pool installed and you’ve been using it for a while, you might notice that it is getting cloudy. But, who wants to dive into a cloudy, murky pool? A swimming pool is only enjoyable when it is clean and clear. Plus it can be dangerous if you are unable to clearly see the bottom. There are a number of reasons your swimming pool water can become cloudy, and there are also easy ways for you to clear it up so your pool can be safe and appealing.

What Causes Cloudy Swimming Pools and How to Clear Them?

Imbalanced chemicals are the most common reason for cloudy pool water. The term refers to too much or too little chlorine, the pH of the water, calcium hardness, alkalinity, or stabilizer levels. The pH affects cloudiness indirectly by interfering with how the other pool chemicals work.

  • A high pH means calcium does not properly dissolve and scaling and cloudiness appear.
  • A dramatically low pH makes chlorine very reactive which depletes levels allowing bacteria to grow and cloud the water.

Calcium hardness can mean excessive calcium levels which cause scaling when it accumulates. The only way to lower calcium hardness is to partially drain your pool and refill making sure to keep the calcium hardness level between 200 and 400 ppm. The more direct causes of cloudy pool water include:

  • Low Free Chlorine: The most common cause of cloudy pool is low free chlorine (FC) level. Free chlorine is that which is available to sanitize your pool water as opposed to combined chlorine which has already been used up or is diluted with ammonia in the water. A low FC reading means you have combined chlorine in the water which causes a cloudy appearance and unpleasant odor. If the FC reading is below 3ppm then you need to shock your pool right away to restore proper chlorine levels and kill bacteria.
  • Ammonia: When free chlorine levels drop to zero or when you have very high combined chlorine (CC)levels you could have an ammonia problem. Excess ammonia in the water will cause a cloudy appearance. When FC levels do not rise after adding chlorine to the water, you can be assured that ammonia is likely the culprit. To correct this, you will need to add a lot of chlorine to the pool to clear the ammonia out.
  • Algae: The buildup of algae is another common cause for cloudy pool water. You can perform an Overnight Chlorine Test to determine if you have algae or not. Add chlorine to the water in the evening and then take an FC reading in the morning. If the levels have dropped by 1ppm then you have the start of an algae problem which causes cloudy water as it is developing.

Most pool shops carry easy-to-test kits that allow you to test all chemical levels. The best kits are those that test for all chemical levels at once as this is more efficient and help you discover the problem quickly.

Cleaning the Pool Filtration System

Sometimes chemical imbalances are not the problem. Cloudy water can be caused by a clogged or dirty filtration system. When water is unable to properly circulate, bacteria and debris can accumulate causing a cloudy appearance. To clean your filtration system and keep your water clear:

  • Ensure all return fittings are turned down so water at the bottom can properly circulate!
  • Make sure your pump is the right size for the amount of water!
  • Most pool systems need to run 24/7 to be effective.
  • Regularly remove particles that are clogging the filter.
  • Regularly clean and replace the filter cartridge (approximately every 1 to 2 years).

It is also important to remove particles from the pool by scrubbing or vacuuming. Too much debris along the walls and floor can contribute to algae growth and cloudy water. Dirt, sunscreen, and body oils are all potential contaminants that can cloud water. Use nets to remove particles that are visible and a pool clarifier for those that are not. Vacuuming the sides and floor of the pool will also remove bacteria, dirt, and algae and this needs to be done regularly too.


Water that is murky likely does not look appealing and certain bacteria or algae can cause infection. It is best to keep your pool clean by maintaining chemical levels and following routine cleaning practices. To have the cleanest and safest pool be sure to regularly maintain chemicals, test chemicals, and clean the filters all year round.


Keep your swimming pool secure with a Guardian Pool Fence