What Causes Cloudy Pool Water and How do You Clear It? - Sutro, Inc

What Causes Cloudy Pool Water and How do You Clear It?

The most common causes of cloudy pool water are improperly balanced water chemistry, insufficient water filtration, environmental conditions, and the addition of granular or powder chemicals. Patience is a virtue when it comes to clearing cloudy water, but through the process of elimination it can be done. It is important to understand the root cause of your cloudy water and not just treat the symptom. 

Improperly Balanced Water Chemistry


When free chlorine is allowed to dip below recommended levels microorganisms such as algae and bacteria can cause water to cloud, turn murky or even turn green. Some common causes of low free chlorine are dilution due to heavy rainfall, organic contaminants, and low stabilizer (CYA). Last but not least, and the easiest of all to fix, is failing to maintain proper chlorine levels. 

When chlorine falls below recommended levels the water should be shocked. Once the pool is free of microorganisms, chlorine should not be allowed to fall below the minimum recommended level and water should be properly balanced to maintain effective sanitation and water clarity.


pH impacts chlorine’s ability to sanitize and can result in requiring a higher level of chlorine to be effective. High pH can also enable calcium to precipitate from solution and cause clouds of calcium carbonate in your water.

pH should be lowered or raised to keep between 7.2 and 7.8 ppm to support effective sanitation and water balance.


High alkalinity can cause cloudy water by allowing pH to bounce, enabling precipitation of calcium and decreased chlorine effectiveness as previously mentioned.

Alkalinity should be adjusted to be within acceptable levels.

Calcium Hardness

High levels of calcium can react with high pH to cloud water and if left untreated it can also cause scaling. High calcium levels can also cause clouding when water temperatures are above 85 degrees Fahrenheit.

Calcium hardness can be lowered by replacing a portion of your water, assuming you do not have a high level of calcium in your fill water.

Insufficient Water Filtration

Pump Run Time

Your pump should run long enough each day to filter the debris and fine particles from your water. On average, typical run times are anywhere from 8 to 12 hours per day depending on the size of your pool (or spa) and your specific equipment.

Increase pump runtime to increase water filtration.

Dirty or Malfunctioning Filter 

There are several types of filters such as Diatomaceous Earth (DE), sand, and cartridge. One thing in common to all filters is that they need maintenance and need to be cleaned periodically. 

Consult manufacturer guidelines on how to maintain your specific filter, which can include backwashing, disassembling, and cleaning of grids or cartridges, or replacing media such as sand or DE.

Environmental Factors


Rain is wonderful and helps keep landscapes lush and green, but it can also make your pool (or spa) lush and green. Rain can dilute chlorine, CYA, pH, and can also introduce minerals, sand, mud and other contaminants that reduce water clarity. Contamination combined with the dilution of chlorine and pH can lower sanitation effectiveness and allow algae growth and cloudy water.

Prepare your pool (or spa) prior to rain if possible by balancing your water and increasing your chlorine level. After the rain is gone, run your filter continuously to filter out particles until your water is clear. You can also use floc or clarifier depending on your specific needs and timeline as well. If you didn’t raise your chlorine level in advance, balance your water chemistry to proper levels and consider shocking to give your chlorine a boost.


Both 4 legged and 2 legged swimmers can introduce a multitude of contaminants, both organic and inorganic. A few examples are sunscreen, lotions, soaps, food, and waste. 

Plan in advance to have shock on hand. Once you are finished with your pool  (or spa) party balance your water, shock, and run your filter continually until

the water is clear. You can also use floc or clarifier depending on your specific needs and timeline.

Check the skimmer baskets prior to shocking – you never know what you may find. Cupcakes and clothes are some of our favorites.

What’s in your skimmer basket?

Addition of Chemicals

(There are several other chemicals that can result in cloudy water, but these are three most commonly observed.)


Powder or granular shock can cause cloudy water due not being completely dissolved. This could be due to multiple reasons such as water temperature, inadequate premixing or simply because it’s an expected event to some extent.

If your water is cloudy after adding dry shock, wait it out and keep your pump running until the water clears. This typically should occur within a few hours, but depending on various factors such as the quality of the product, circulation, and filtration it can take overnight or longer.


Algaecide that contains copper can also cloud water, and if used with a high level of chlorine can cause a chemical reaction that results in green water and/or green hair for fair haired swimmers. Copper and Iron can also be introduced by your fill water (well water typically contains a lot of metals and minerals). 

If your water is cloudy after adding algaecide, wait it out and keep your pump running until the water clears. 

If your water turns green very shortly after adding algaecide that means that a high dose of chlorine oxidized the copper from the algaecide. You should avoid high chlorine levels when the level of copper in your water is greater than ~.2ppm. To clear the green tint, you can use a chelating or sequestering agent to bind the copper in solution, or you can use a product that binds the ions and removes them completely from your water.

Phosphate Remover

Phosphate removers can also cause cloudy or hazy water as they bind to phosphates and cause them to fall out of solution and precipitate for removal by filtration.

If your water is cloudy after using phosphate remover, continue to follow the product instructions and wait it out. Keep a close eye on your filter pressure in the following day’s damage could occur if the pressure is allowed to get too high. You will likely need to clean your filter to lower the pressure within 24 to 36 hours after treating your water.

Guide to Clearing Cloudy Water in Your Pool

  1. Analyze your current situation, what happened to make the water cloudy? Was it rain, did you add any chemicals, did you have a party? 
  2. After assessing the situation to get some ideas of what may be causing your issue, check your water chemistry.
    1. If water is balanced and free chlorine is within range then clean/brush/filter and wait it out for a bit. Consider floc or clarifier.
    2. If water isn’t balanced and/or free chlorine is low then balance water and shock. Clean/brush/filter and wait it out for a bit. *If you see algae as well, wait 24 hours after shocking and you can add algaecide, or you can continue to hold water at shock level until you get rid of algae. Remember to brush daily while eliminating an algae infestation.
  3. Check that your filtration system is functioning properly, when was it last cleaned, what is the pressure, are there any visible reasons it could be malfunctioning (media is old, the filter is dirty or clogged, run time isn’t sufficient et cetera).
  4. Wait it out for a bit, keep testing your water, and look for signs that you are making progress. Take pictures to compare day by day. *Bonus, with pictures you can show people how much of a pool (or spa) pro you are now.
  5. Prevent yourself from having to go through so many steps to clear cloudy water in the future, understand the root cause, and address it so that it doesn’t occur again. Likewise, if it does occur again then understand how to address it quickly before it gets out of hand.
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