7 Causes of Cloudy Swimming Pool Water and How to Clear it
Cloudy Pool Water: Causes, Treatment, and Preventive Measures
Cloudy or milky swimming pool water is caused by 7 main issues and they are; 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.
7 Ways to Clear a Cloudy Pool Water
- Balance free chlorine(FC) levels
- Eliminate ammonia
- Get rid of young algae
- Monitor and balance pH and TA levels
- Correct Calcium Hardness levels
- Backwash filter or replace filtering agent
- Remove foreign particles, scrub, and vacuum up the pool
Start by Taking Free Chlorine Reading and Balance it
The first and most common cause of cloudy water is low free Chlorine(FC) level. Low free chlorine indicates you have chloramine (combined chlorine) that turns water cloudy, smells more of chlorine, and cannot sanitize your pool water by killing harmful germs and bacteria causing algae and ammonia.
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 0.5ppm, whether 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 pumps run-time will not help much in clearing cloudy water, and you have to shut down your SWCG and shock your saltwater pool manually using harsh chlorine just like non-saltwater pools, use the link 'shock your swimming pool' in the previous paragraph and findout how you can shock your saltwater pool.
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 0ppm, very high CC levels, and high demand for chlorine in your water but FC level 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 Overnight Chlorine Lose 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 FC reading the following morning; if FC level drops by more than 1ppm 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 maintaining FC level.
More Reasons why your Pool is Cloudy?
- Imbalanced chemicals: An improper chemical balance might mean there is too much or too little chlorine, the pH, alkalinity, calcium hardness, or stabilizer(Cyanuric acid)
- Faulty filter: Poor filtration means you might not be running your filter long enough, clogged or worn out filter cartridges, scaling on filter, which all result in poor water circulation.
- Environmental factors and debris (particles): 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 nitrates, phosphates, and other chemicals into your pool that may make your water cloudy.
How wrong or Imbalanced Pool 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 processes 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 causing 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 level between 200 and 400ppm all the time.
- Other Chemical imbalance: 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, and you might end up with severe 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 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. LaMotte ColorQ Pro 11
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.
Ideal Chlorine Levels
Total chlorine should be 3 ppm and Combined Chlorine should always be below 0.5 ppm (or 0 ppm if possible) to avoid chloramine.
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 is the best option for 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. Sodium Hypochlorite
How to Know If 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 make water look dull and 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.
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 the sand filters. Here is my detailed guide on types of pool filters, how to select the best one, and how to properly maintain it.
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.
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 pool clarifier to clear up the water when cloudiness persists. Also, I prefer using and vacuuming the pool to do away with fine particles that cannot be removed by leaf net or clarifier. pool flocculant
- 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, paying close attention to the chlorine levels, and adjust them as appropriate.
5. Can I Use Algaecide to Clear Cloudy Pool Water?
You can use 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, clean using a large leaf net, vacuum and kill it 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 algaecide which can be very expensive and best result is not guaranteed like when you use liquid chlorine. Some algaecide 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.
The main cause is usually imbalanced chemicals. If your water is free of algae, all you need to do is test for all the chemicals and adjust. Starting with the pH, then the chlorine, and then other chemicals after that.
If the water still appears cloudy after adjusting all the chemicals, you can try using either water clarifier to remove the debris through the filter or use pool flocculant and then vacuum to remove any particles.
Why Is the Pool Water Still Cloudy After Shocking and/or Adding Algaecide?
In most cases, your pool water may still be cloudy but FC is fine or high. Cloudy or milky water after shocking is normal, and the water should clear up within an hour or so. Just make sure your pump and filter are running properly.
If you add algaecide, keep in mind that some algaecide contains copper, which can actually make a pool cloudy. If the cloudiness persists 24 hours after shocking, then it's possible that you used a poor-quality chlorine shock. In this case, you should take another reading of free chlorine and do the shocking again using liquid chlorine(Sodium Hypochlorite).
You should also check that all chemicals—especially pH, total alkalinity, cyanuric acid, and calcium hardness—are within the recommended levels, and remember that Calcium Hypochlorite chlorine shock and chlorine tablets are not recommended for daily pool sanitization because they raise calcium, pH, and Cyanuric acid in your water and you need to be extra careful when using them or else these chemicals will get off the chart causing cloudy water, algae, or ammonia in the long run.
Finally, debris could cause continued cloudiness in the water even when chlorine level is fine. You can try using a water clarifier to send all the particles to the filter, or you can use pool floc to gather all the debris together and then vacuum it up using a manual pool pump.
Why Is the Pool Cloudy After a Rain?
Rain water brings dirt, mud, dust, and other contaminants that contain phosphate, which breeds algae. With the presence of phosphate, the water will start to become cloudy even before the algae begins to grow. If you know a storm or shower is about to come, make sure there is ample chlorine to counter the dilution that rain water will bring, and have the filter running during the rain.
Why Is My Pool Cloudy When the Chemicals Are Balanced?
When all the pool chemicals are fine but your water is still cloudy, there is a good chance that you have particles in your pool. In this case, a is used to collect all the fine particles so that they can be picked up by the filter. water clarifier
Alternatively, you can use pool floc (flocculant), also known as a super floc, which is a chemical that is used to bring all the clouding particles to the bottom of your pool forming a large cloud that you can then vacuum up using a manual pump. The particles collected using a pool floc will not pass through the filter like they would if a water clarifier were used. Make sure that your filter is set on the backwash or waste option when you are vacuuming to avoid any damage that may happen to the filter as a result of clogging.
Can You Use Baking Soda to Clear Up a Cloudy Pool?
NO! Baking soda is a base and will hugely increase the level of pH, which actually causes the water to turn cloudy. Some people may suggest using baking soda as a quick fix if alkalinity is high, but it is not a reliable pool chemical. Chlorine should be the only substance used to clear a cloudy pool.
Is It Safe to Swim in a Cloudy Pool?
You shouldn't swim in a cloudy pool for several reasons:
- If you can't see the bottom of the pool, struggling swimmers will also be hard to spot, making the risk of drowning much higher.
- Cloudy pools are full of bacteria and pathogens that can cause urinary tract infections, stomach problems, and eye irritation. The most common bacteria found in cloudy or dirty pool water is E. coli.
- It's just plain disgusting. A cloudy pool is an indication that the water contains high amounts of dirt, body oil, sunscreen, spit, urine, sweat, and other gross particles.
Which tool do you use to measure and control your pool chemistry?
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
I have been cleaning up a severely neglected pool and still have cloudy water and barely any visibility. I've been keeping chlorine levels as best as possible while lowering the pH to 7.0 but nothing helps. Any advice?
I think there is a problem with your chemicals. Use an accurate test kit and take a reading of all the chemicals especially pH, Alkalinity, and Calcium hardness. Chlorine cannot balance when other chemicals especially pH is not within the recommended range and might be the reason why your water is cloudy. Your pH is a little lower and it should be between 7.4 and 7.6. So make sure you take accurate readings and adjust all chemicals before adding chlorine.Helpful 34
My pool has been cloudy for four days now. I've done all the chemicals, vacuuming, backwashing etc. What do I do now?
Counter check if your chlorine is balanced. Make sure your free chlorine is 3 ppm, and combined chlorine is 0 ppm. If not, add more liquid chlorine. Also, you can use pool clarifier, or add pool flocculant first and then vacuum if that will work out for you.Helpful 34
Cloudy material settles to the bottom of pool. When vacuumed, it comes back into the pool through the return inlet completely nullifying the vacuum process. What should I do?
Cloudy material coming through the return jets might be caused by two issues; sand sediment from your filter and air bubbles.
If it's sediment means, it means your filter is faulty and you need to replace your cartridges or clean your filter.
However, if it's bubbly, that is normal especially within few days of pool opening and will rectify soon. Air bubbles passing through the returns sometimes leads to poor filtration and that might be the cause of cloudy water coming to your pool through the jets.Helpful 30
Why do people put baking soda in their pools?
Baking soda is used as an agent to increase pH and Alkalinity level when lower than recommended.Helpful 29
I have a 15 X 52 size above ground pool, the water was getting green so I added two 1lb bags of shock and turned on the filter but the water is still cloudy. I think I was supposed to add one bag instead of two. Will it clear up by itself? Do I need to add something else to fix this?
If your pool was green, it means you had algae. I don't know your chemicals readings and it could have been better if you included readings for FC, Cyanuric acid, pH, TA, and CH.
Also, you need to use liquid chlorine (sodium hypochlorite) since it won't affect your pH and Calcium hardness like Calcium hypochlorite and your pH and Calcium might get off the chart making your water more cloudy, but if you know what you are doing it's fine.
If you reached the recommended shock level in relation to Cyanuric acid level then your water will finally become clear. If it doesn't become clear within 24 hours then you might be having debris, ammonia, or algae is still present in your pool and you have two options:
1. Brush the walls and bottom of your pool then use poolfloc to collect any debris at the bottom of the pool then vacuum the pool to remove all dirt.
2. If it's not clear after brushing and vacuuming it, chances are high that you have ammonia or algae is still there: Test pH and lower it to around 7.2 if it's more than 7.4, then use liquid chlorine (preferably) to raise your FC to around 12ppm with cyanuric acid level of 30ppm, watch how FC will work by testing your FC level after 30 minutes, if FC drops below 4ppm quickly raise it back up to 12ppm and repeat the process until FC becomes stable between 4-6ppm, leave it to come down to 3ppm then raise Cyanuric acid to 40ppm and your water should come clear.
Make sure you balance all the other chemicals in your water including Calcium hardness.Helpful 28