Causes and Cures for Cloudy Water


We get calls, emails, and comments about cloudy water all the time. It’s one of the most common problems in a swimming pool, and the reasons for cloudy water are almost endless. Here, we’ll walk you through the most common causes of cloudy water and what you can do to cure it.

The first step is to decide what type of cloudy water you have–what color is it? We’ll break it up into three color categories to help you begin to narrow down the cause: milky water, green water, and rusty water. Identify what color your water is and let’s get started! Keep your test strips handy; they’ll help a lot as you work through determining the cause of your cloudy water.

Milky Water

If your swimming pool water is milky like this one, there are four likely causes.

  • The first possible cause is small, suspended particles in the water. This is typically caused by high pH or high alkalinity–dissolved minerals can “precipitate,” or come out of solution in the water and transform into small, solid particles. To remedy this, you’ll need to lower your pH or alkalinity. There are a number of products you can use to lower alkalinity and pH. We recommend Pool Solutions. Follow package instructions to lower the pH or alkalinity to the proper level (here’s where it’s important to know your current reading, so you can use the proper amount of product!) Important note: never put the whole amount in at one time; we recommend the rule of halves. For example, if you have determined that you need 10# of pH-, put 5# in to start. Let the pool run for a day, and then test the water again. If the pH is still high, add half of the remaining dose (2.5#). Wait another day and check the water clarity and chemical levels. Water is incredibly responsive, and it always seeks to balance itself. The prescribed dose of chemicals is often too much, leaving you with an over-correction and the
    opposite problem than you started with. 
  • The second possible cause is a buildup of dirt and pollution as a result of poor filtration or not enough chlorine. To remedy this, backwash your filter and shock your pool. You can add a clarifier when you’re finished to add a little extra polish to your water.
  • This third possible cause is over-stabilized water. Stabilizer is an important part of the chemical makeup of your pool; it keeps the chlorine from being zapped by the sun and helps keep your pH level stable. However, too much stabilizer in your water can reduce the effectiveness of your chlorine, increasing the time it takes to kill the organisms that cause haziness and cloudiness. To remedy this, you’ll need to remove some of the water from your pool and replace it with fresh water. You can remove water from your pool by performing an extra-long backwash through your filter. Be sure you don’t completely empty your pool–you should only need to remove a couple of inches to fix your problem.
  • The fourth possible cause is a blocked or ineffective filter. Whether you have a sand, cartridge, or DE filter, you’ll need to service it every so often. Sand and cartridges need to be replaced eventually, and a DE filter will need to be cleaned. This is on top of your normal backwashing routine. If this is a recurring problem for you, and you’re having to service your filter more often than you used to, it might be time to replace the filter. Call your local pool company if you’re not sure.

Green Water

If your pool is green, the most probable cause is algae. Algae forms when there is not enough chlorine in the pool, as chlorine keeps algae from growing. Your chlorine has probably either fallen below the necessary level, or has become ineffective. The quickest way to fix this is to shock your pool–the high dose of chlorine will kill the algae quickly. You can also use an algaecide. After adding the correct dose of chemicals, be sure to brush the surfaces of your pool, paying extra attention to easily-missed spots like behind ladders and around the light. 24 hours later, backwash your filter to fully remove the algae.

Rusty Water

The most probable cause for rust-colored water is iron or other metals. Important note: sometimes iron can turn water a greenish color, too. You’ll want to take action on this quickly, as iron can stain your pool surfaces. Our absolute favorite product  for removing iron from swimming pool water is Ferri-Tabs. They’re the most effective product we’ve ever seen at removing iron–it’s truly incredible. If the iron in your water has settled onto the surface of your pool, you’ll need to use a stain remover to get it back into the water. Once the iron is in solution, drop the recommended number of Ferri-Tabs into your skimmer (1 tab per 3,000 gallons). Let your pool run for 24-48 hours, and then backwash your filter. Your pool should be sparkling clean and ready to swim!