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7 Causes of Cloudy Swimming Pool Water and How to Clear It

Barack has expertise in pool chemistry and pool maintenance. He writes in-depth articles about how to maintain pools for optimal enjoyment.

How to Fix Cloudy Pool Water

How to Fix Cloudy Pool Water

Cloudy Pool Water: Causes, Treatment, and Preventive Measures

Cloudy or milky swimming pool water is caused by seven main issues: improper levels of chlorine, imbalanced pH and alkalinity, very high calcium hardness (CH) levels, faulty or clogged filter, early stages of algae, ammonia, and debris. This article will cover the seven main ways to clear that cloudy water and get your healthy pool back.

7 Ways to Clear Cloudy Pool Water

  1. Balance free chlorine (FC) levels.
  2. Eliminate ammonia.
  3. Get rid of young algae.
  4. Monitor and balance pH and TA levels.
  5. Correct calcium hardness (CH) levels.
  6. Backwash filter or replace filtering agent.
  7. Remove foreign particles and mineral deposits, scrub, and vacuum up the pool.

Start by Taking a Free Chlorine Reading and Balancing It

The first and most common cause of cloudy water is low free chlorine levels. Low free chlorine indicates you have chloramine (combined chlorine) that turns the water cloudy, and smells more of chlorine. With too much chloramine, the chlorine cannot sufficiently sanitize your pool water by killing harmful germs and bacteria, so algae and ammonia grow rapidly.

As such, if your pool water is cloudy, the first thing you should do is to measure your free or combined chlorine; you can get the value of combined chlorine by deducting the value of FC from Total Chlorine.

If you have your FC below 3 ppm or combined chlorine (CC) above 0.5 ppm, whether it's a saltwater or non-saltwater pool, FC is low and you need to shock your swimming pool immediately to fix cloudy water and kill bacteria before you get algae or ammonia in your pool.

If you have a saltwater pool and it's cloudy, the damage is already done, and raising the percentage setting in your saltwater chlorine generator (SWCG) or your pump's run-time will not help much in clearing cloudy water. You have to shut down your SWCG and shock your saltwater pool manually using harsh chlorine just like non-saltwater pools.

Could It Be Ammonia or Algae Starting Up?

In rare circumstances—especially during the beginning of summer when swimming pools are opening after closing for winter—your pool may have severe cloudy water that is difficult to clear. FC and cyanuric acid levels drop to zero or close to 0 ppm, there are very high CC levels, and there is a high demand for chlorine in your water, but FC levels will not rise easily, even after adding a lot of chlorine. If you notice these signs in your swimming pool, you have ammonia and you need to use a lot of chlorine to get rid of ammonia in your pool.

Early stages of algae make pool water look cloudy and dull. To be sure it is not algae starting up, perform an overnight chlorine loss test (OCLT), which is done by adding chlorine to pool water in the evening when the sun is down to avoid depleting FC and taking the FC reading the following morning. If FC levels drop by more than 1 ppm through the night, the result is positive, and you have algae starting up—and the sooner you get rid of the algae the better. Ammonia and algae come as a result of low FC levels, and the only way to keep them away from your pool is to maintain proper FC levels.

More Reasons Why Your Pool Is Cloudy

  1. Imbalanced chemicals: An improper chemical balance might mean there is too much or too little chlorine, or the pH, alkalinity, calcium hardness, or stabilizer (cyanuric acid) levels are imbalanced.
  2. Faulty filter: Poor filtration means you might not be running your filter long enough, you have clogged or worn-out filter cartridges, or there is scaling on the filter, which all result in poor water circulation.
  3. Environmental factors, debris (particles), and minerals deposits: Dust, pollen, and leaves can build up in your filter and impede the cleaning process. Insects, bird droppings, and run-off water after a storm or rain also contribute to cloudy pool water. Run-off water brings in minerals including nitrates, phosphates, silicates, and sulfates into your pool that may make your water cloudy.

Wrong or Imbalanced Chemicals Cause Cloudy Water

Pool chemistry is the trickiest part of pool management. Using wrong chemicals or adding incorrect amounts are the major causes of cloudy water and may even lead to algae if extra care is not taken.

  • Improper pH and chlorine levels: These are the most common culprits. The pH is not directly associated with cloudiness in the water, but it affects how chlorine and other chemicals work in your water. Very high pH usually leads to calcium not dissolving properly, causing cloudy pool water and calcium scaling both in saltwater and non-saltwater pools. On the other hand, if your pH gets too low, chlorine becomes very reactive and depletes very fast, forming lots of combined chlorine (chloramine), which turns the water cloudy and is ineffective in killing bacteria, algae, and other microorganisms in your water.
  • High total alkalinity (TA): You also need to closely monitor changes in the level of TA. A high TA causes pH and calcium scaling, both of which are associated with cloudiness. The process of lowering total alkalinity involves aeration after adding muriatic acid. This process raises the pH to recommended levels.
  • High calcium hardness: Very high calcium hardness levels in pool water will lead to excess calcium, which can't dissolve in water and accumulates in your pool. This causes cloudy water that won't clear up and calcium scaling inside the pool, and sometimes scales might clog your filter—leading to poor filtration and dirty or cloudy water. The only way to lower CH levels is to partially drain and refill your pool water. As such, remember to keep CH levels between 200 and 400 ppm all the time.
  • Other chemical imbalances: High levels of accumulated phosphate and bromine and imbalanced stabilizers, such as cyanuric acid (CYA) might also cause cloudiness. If you are using cyanuric acid often, make sure that the CYA and free chlorine levels are balanced, because excess CYA will significantly reduce free chlorine. You might end up with severely cloudy water when bacteria converts cyanuric acid to ammonia. Use this chlorine/CYA chart to determine proper FC to CYA levels for your pool.

How Do I Know Which Pool Chemical Is Imbalanced?

In order to verify which of these chemicals might be imbalanced, you need an accurate, fast, and easy-to-use test kit. I use the LaMotte ColorQ Pro 11 digital water test kit. It saves me lots of time as it is easy to use and very effective for frequent use. It tests pH, free chlorine, combined chlorine, total chlorine, bromine, calcium hardness, total alkalinity, cyanuric acid, and other metals including iron, copper, biguanide, and biguanide shock all at a glance.

I then use PoolMath by TFP to find the exact amount of each chemical to add. Ideally, the recommended chlorine levels should be around 3 ppm, which should be the same as the total chlorine if chloramine is at 0 ppm.

What's the Difference Between Free Chlorine, Combined Chlorine, and Total Chlorine?

Free chlorine refers to the available chlorine that can sanitize your water. It differs from "combined chlorine," which is chlorine that has already been used up, oxidized, or diluted with the ammonia and nitrogen compounds in the water. Unlike free chlorine, combined chlorine is ineffective after disinfecting and killing microorganisms. Total chlorine is the sum of free chlorine and combined chlorine.

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Read More From Dengarden

Ideal chlorine and combined chlorine to avoid chloramine in your pool.

Ideal chlorine and combined chlorine to avoid chloramine in your pool.

1. How to Clear Cloudy Pool Water Caused by Low Free Chlorine

Low free chlorine levels are caused by heavy usage, heavy rainfall (which dilutes the chlorine), or hot sunny days when UV light oxidizes lots of free chlorine. If you have an outdoor pool, you can use a chlorine stabilizer, such as cyanuric acid, to prevent chlorine depletion as a result of direct UV light. Remember that cyanuric acid is very strong, and if it exceeds the recommended levels, free chlorine will disappear, and the water will turn cloudy and be at high risk of algae growth.

In summary, if your combined chlorine reads above 0.5 ppm, your water may turn cloudy and become unsafe for swimming. If this is the case, you need to shock your pool immediately to clear it.

Liquid chlorine or sodium hypochlorite is the best option for a daily free chlorine boost, because it does not affect pH, calcium hardness, and cyanuric acid in your water, which make pH, calcium hardness, and cyanuric acid scale high above the recommended levels—leading to cloudy water, metal stains, ammonia, algae, and other pool problems.

How to Know If Your Chlorine Is Imbalanced

The wider the range between free and total chlorine, the more combined chlorine (chloramine) is present in the water. Combined chlorine should always read below 0.5 ppm or just 0 ppm, if possible. This means you should test chlorine levels on a daily basis and adjust it as appropriate before there's excess chloramine, especially during the summer when it's hot and the pool is used heavily.

Safe pH Level for Swimming

The correct level of pH in a swimming pool should be between 7.4 and 7.8, with 7.6 being the ideal level.

2. Monitor pH and Total Alkalinity

The level of pH in pool water affects how all other chemicals function, including chlorine. When pH level gets too high, chlorine will become ineffective, and we all know how important chlorine is in a pool. High pH also makes water look dull, and it should always be within the recommended range.

How to Balance the pH in Your Pool

To lower pH, you need to use a pH reducer (pH minus), such as muriatic acid or sulfuric acid. Anything below a pH of 7.0 is too low, and apart from turning water cloudy, this environment brings about harmful bacteria causing ammonia and algae.

To increase low pH levels, you need to use a pH Increaser (pH plus) with soda ash.

How to Balance Total Alkalinity (TA)

Finally, ensure that total alkalinity is within the required range of 80 ppm and 120 ppm to avoid bringing up pH levels and causing calcium scaling. To lower total alkalinity without extra equipment, add muriatic acid and aerate the pool to restore pH levels without having to add a pH increaser, which will increase alkalinity levels too.

3. Clean the Pool Filtration and Circulation Systems

A poor water-circulation system can also be a big problem. If your water cannot circulate properly, it will become stagnant and cloudy. To fix this problem:

  • Ensure that the return fittings (eyeball fittings) are turned to point down, which enables the water at the bottom of the pool to circulate properly. However, the circulation system will largely depend on how the pool was built.
  • Make sure you are using the right pump size to adequately clean the water.
  • Make sure the filtration system is running long enough. A filter should run 24/7 for the water to remain clean all the time. However, for home pools that are not busy, at least 8 -10 hours a day might suffice.
  • Remove particles that may be blocking your filter. Your filter system continuously cleans the water, and if it does not function properly, the water becomes dirty, cloudy, and may even develop algae. Large particles are fond of blocking filtration systems, especially diatomaceous earth (D.E) and cartridge pool filters.
  • Ensure that you regularly clean, backwash, or replace the D.E and cartridge filter medium as appropriate. Cartridge filters usually last 2,000 hours and should be replaced every 1-2 years, depending on usage.

Which Pool Filter Is Best?

There are three types of filters: DE (diatomaceous earth), cartridge (paper), and sand. Each has its own pros and cons. A DE pool filter is the most efficient when it comes to filtration, followed by cartridge, and sand filters.

Private Pools

DE and cartridge filters are recommended for home pools and may not be the best when it comes to public pools (apartments or hotels) due to their tendency to clog. The filter medium for DE and cartridge filters also require frequent replacement.

Public Pools

A sand filter is always best when it comes to public or semi-public swimming pools, but the sand used in a sand filter also gets clogged and becomes ineffective, which may cause your water to be cloudy or dirty. Consequently, the sand should be replaced every year.

4. Remove Foreign Particles, Scrub, and Vacuum the Pool

The environment and weather may also be the cause of cloudy water. To fix and prevent cloudy water, follow all of the best practices below.

  • Foreign particles, small and large, may find their way into the water, especially during spring. Body oil and sunscreen from swimmers also washes off in the water and accumulates in the pool, causing cloudiness. You can use nets to remove visible particles, and you may have to use a pool clarifier to clear up the water when cloudiness persists. Also, I prefer using pool flocculant and vacuuming the pool to do away with fine particles that cannot be removed by leaf net or clarifier.
  • Algae also causes cloudiness in its early growth stages. To remove algae, scrub and clean the pool using a large leaf net and vacuum: Then do a pool shock to get rid of any remaining algae. Control the amounts of pH, chlorine, TA, phosphate, and other pool sanitizers to prevent algae growth.
  • Free chlorine depletes more quickly in full sunlight, but if trees and buildings are next to your pool, direct sun will be blocked. If your pool is in direct sunlight, consider using a chlorine stabilizer (CYA) and a pool cover when not using the pool.
  • Rain also contributes to cloudy water because it dilutes and therefore reduces free chlorine levels. All you have to do is test the chemicals, pay close attention to the chlorine levels, and adjust them as appropriate.

5. Can I Use Algaecide to Clear Cloudy Pool Water?

You can use an algaecide to kill early stages of green algae that might make your water appear cloudy, but the best method of getting rid of algae is to scrub and clean your pool using a large leaf net, vacuum, and kill algae with liquid chlorine shock.

You should only use algaecide once in a while for preventive measures and when green algae is just starting to show up—it is not useful when algae outbreak is immense and very visible.

Furthermore, if you have full green, black, or yellow algae, you may end up using a lot of algaecide, which can be very expensive and the best result is not guaranteed like when you use liquid chlorine. Some algaecides may also cause foaming or deposit copper metal in your water when used in large quantities.


Why Is My Pool Water Cloudy After Opening a Pool?

Depending on how carefully you closed the pool for the winter, at the beginning of summer, you may see algae and cloudy water.