What Causes Cloudy Pool Water?

Pools get cloudy for a number of reasons. This article will discuss several of them, but keep in mind you could have a combination of these factors going on. If you need further guidance, contact us, or request an online training with us.

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Water Clarity and Turbidity

Like many kids growing up, I loved going to the pool. At the beginning of the summer, the water was chilly, but clear and beautiful. But as the summer progressed, the water continued to get cloudier and cloudier. It seemed to be the case at every summer pool. I can remember swimming in pools that I could hardly see the tile line on the bottom of the pool.

So what causes pool water to get cloudy?

There are many factors that impact water clarity. A few of them are fundamental, and without addressing those few factors, you can put all the best pool chemicals you want in the water, and it still won’t matter. Pool water maintenance will continue to be an uphill battle against turbidity (cloudiness), even though the pool water chemistry may be well within acceptable ranges. These key factors are often overlooked or misunderstood.

Causes of cloudy pool water

Filtration Problems

There are three crucial aspects of water quality: Filtration, Circulation, and Chemistry. Filtration is a physical process of screening particles out of the water and capturing them. When it comes to cloudy water, filtration is the usual suspect. The filter's job is critically important to a swimming pool. Without good filtration, even perfectly balanced water would look bad.

Not all filters are equal. There are basically three types: sand (pressure or vacuum sand), cartridge, and D.E. (either grids or regenerative D.E.). What the best type for a pool is a matter of opinion, and we try to stay out of that argument. That said, the particle sizes that each filter can capture are different. All of them tend to be able to capture particles smaller than the human eye can see, so you can still have great water clarity with all three types of filters.

Filters are generally rated based on how small of a particle size, in Microns (µ), they can capture.

Particle and filter sizes

But filters can be damaged (like broken DE grids or torn cartridges), or contaminated with organic waste (grease, grime, gunk), which can clump up sand and cause other issues...

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In a sand filter, for example, the water can form channels to better get through the sand bed. The water had to get through the congealed media so it forged a path of least resistance, which circumvented the screening process. That’s bad, because now larger particles can circulate through, when they otherwise would’ve been stopped. It's a cloudy water highway tunnel.

Channeling is a problem unique to sand filters, but clogging problems apply to all filters. Water will find the path of least resistance, so be sure the filters are being maintained and cleaned.


sunscreen in pool water, organic waste, turbidity, cloudy pool water

Organic waste

Non-living organic waste (bather waste) is a huge contributor to cloudy pool water. This includes body waste, oils, saliva, dead skin, sweat and urine. It also includes lotions, cosmetics, and the big one for summer pools: sunscreen. Some components of these contaminants contain Nitrogen compounds like Ammonia and Urea, which require a different chemistry strategy to address.

In the presence of chlorine, organic waste is either oxidized, partially oxidized, or adheres together with other particles in the water. If fully oxidized, the waste is ‘burned up’ and removed from water. Chlorine is not well suited for organic oxidation…its primary function is to sanitize, that is, kill germs and other living pathogens. When chlorine has to do the heavy lifting of oxidizing the organic waste of a busy swimming pool, it usually falls short. This is why Organic Waste and Carbon Management is our Second Pillar of Proactive Pool Care.

dirty-ORP, dirty ORP, ORP probes, cloudy ORP test, turbidity and ORP, dirty ORP probes, clean chemical controller probes, enzymes and ORPThe water gets cloudy not only because these contaminants are eventually visible and refract light, but because chlorine can get overwhelmed, which can lead to reproducing algae and other contaminants. We can measure how effective (or how burdened) chlorine is with Oxidation Reduction Potential (ORP).

Speaking of ORP...cloudy pool water can distort ORP readings. Compound that with non-living organic scum sticking to the probes? It's difficult for the ORP sensor to give you an accurate view of the water's conductivity. At a bare minimum, it is important to keep ORP probes clean.

When chlorine cannot fully oxidize the ammonia, nitrogen and carbon-based contaminants, disinfectant byproducts (DBPs) are formed, like chloramines. Another result is that non-living organics will adhere together or with dirt particles in the water…think about the tile scum line. Since carbon is lighter than water, organic waste floats to the surface usually…but when adhered to heavier dirt, it may stay suspended in the water.  Multiply this reaction several million times over, and you get turbid, cloudy water.


Reproducing Microorganisms

Sanitization is a battle between the killing rate of the sanitizer and the growth/reproduction rate of a given contaminant. Let's take the most common living contaminant for example: algae. The reproduction rate of modern-day algae can be as fast as 3-6 hours, according to some sources. If chlorine is bogged down handling non-living organics and other things, its killing rate may be matched or exceeded by the growth rate of algae. If so, it can mean an outbreak, and possibly cloudy water too. Chlorine can't do everything, yet we depend on it to do so much.

This is why we want to not only optimize chlorine, but also minimize the growth rate by removing micronutrients like phosphates. Phosphate Removal is our Third Pillar of Proactive Pool Care.


Total Dissolved Solids (TDS)

Total Dissolved Solids (TDS) is a measurement of all solids dissolved in water. It includes metals and minerals like calcium, and salt. It also includes chlorides, cyanuric acid, and alkalinity ions. And while these substances are dissolved in water and invisible, high TDS can lead to conditions where water gets cloudy. For instance, high TDS drives the LSI down, which could lead to etching a cement pool finish. That etching could lead to a spiked pH which in turn can precipitate calcium carbonate out of solution. It sounds backwards, but if you understand the LSI, it makes perfect sense.

Side note about salt…if your pool uses sodium hypochlorite (liquid bleach) for chlorine, that's really a form of salt (sodium hypochlorite).  So even if you don’t think you have a “salt pool”, you can still have high levels of salt TDS. That, and another byproduct of bleach is sodium hydroxide, which has a pH of about 13. That can raise pH and also cause calcium to fall out of solution. And in non-stabilized pools, high pH means weaker chlorine (%HOCl), and less effective chlorine can lead to cloudier water when facing bather waste.

TDS continues to climb because of evaporation and accumulation, as well as left-behind byproducts from just about every pool chemical used. Every type of chlorine will eventually be reduced into a chloride (Cl-), which contributes to TDS. Every type of chlorine has a byproduct too, like calcium hardness from cal hypo, salt from liquid chlorine, and cyanuric acid from dichlor and trichlor. All of those byproducts contribute to TDS.

soda ash cloud, soda ash, sodium carbonate, soda ash clouded pool, cloudy pool water, LSI, orendaCalcium Carbonate

When water becomes over-saturated with calcium carbonate (as measured on the LSI), calcium carbonate begins to fall out of solution. This can cause cloudiness, even if it's only temporary until carbonate scale is formed. An examples of this is when you add calcium chloride to a pool with a high pH. Calcium will not dissolve well when the pH is high, so it clouds up the water and eventually falls to the bottom as dust (we call it snowing). 

Another example is more dramatic. If you add Sodium Carbonate (Soda Ash) directly to the pool, it can cloud up the pool entirely. It is calcium carbonate rapidly solidifying out of solution, and it clouds up the pool.

PR-10,000 Phosphate Remover (temporary)

Our concentrated phosphate remover PR-10,000 will cloud up the water when it reacts with phosphates. But this is temporary and a natural part of the reaction. The precipitate should be filtered out or vacuumed to waste.

Best Practices for Water Clarity

  • Optimize chlorine by supplementing it with either enzymes, secondary systems like Ozone/UV/HDO, or both.
  • Regularly backwash, clean and maintain filters to avoid channeling and other problems
  • If you have cloudiness that is small enough that it's still passing through filters, consider using a clarifier to bind particles into larger clumps for easier filtration
  • Manage the LSI and maintain good calcium levels. If using soda ash, pre-dissolve in a bucket of water and add slowly, rather than just throwing the powder into the pool directly.
  • When CYA, nitrate, metal or TDS levels get too high, drain and dilute some of your pool with fresh water.
  • Keep phosphates to a minimum to slow the growth rate, and help chlorine stay ahead of reproducing contaminants

Any pool can have world class water clarity. Why not yours?

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