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. There are three distinct types of water clouding: water quality issues (green, yellow, or brown cloudiness), water balance issues (pure white or gray), and chemical conflicts (usually bubbly or films floating around on the surface).
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 warmer and cloudier. It seemed to be the case at every summer pool. I can remember swimming in pools where I could hardly see the tile line on the bottom of the pool. It was gross.
So what causes pool water to get cloudy?
Great water clarity requires good circulation, filtration, and chemistry. And within chemistry, this article will examine how water clarity is affected by water quality, water balance, and pool products.
There are several potential causes of cloudy pool water, both in terms of water quality and water balance. There may also be temporary cloudiness from chemicals and products used.
Water quality issues include pool filtration problems, non-living organic waste, oils, tannins, and other hydrocarbons incompletely oxidized by chlorine, and reproducing microorganisms like algae. Water quality issues tend to cloud the water green, yellow, or brown in color.
Water balance issues are usually calcium carbonate clouding (high-LSI violation), or some variation therein. More often than not, carbonate alkalinity is high enough to create a high pH ceiling that causes an LSI violation during the week. This also leads to issues like calcium flakes in saltwater pools. Water balance issues cloud the water pure white, or gray. This is because it's calcium carbonate (CaCO3) coming out of solution.
Pool products can sometimes conflict and cause cloudiness, like enzymes versus poly products (like polyquat algaecides and polymer clarifiers). Some products, like phosphate removers, will temporarily cloud the water as they precipitate inert phosphate dust. Calcium Hypochlorite (chlorine) and soda ash can also cloud a pool because of their high pH, which causes a high LSI locally.
Let's explore each of these factors.
Filtration is the physical process of screening particles out of the water and capturing them. Poor filtration is a common culprit when the water gets cloudy or dirty. Without good filtration, even perfectly balanced water can look bad. There are three basic types of swimming pool filters.
All three types of filters are capable of capturing particles smaller than what the human eye can see, so you can still maintain excellent water clarity with any of them. Each filter has a different screening ability measured in microns (µ), with D.E. being the finest, followed by cartridge, and then sand.
Damaged or fouled filters will eventually fail to deliver clear water. Water will force its way through the filter media following the path of least resistance. If water can bypass the filter in this way, its particles also bypass the filter, rendering the filter ineffective.
D.E. filters may have a cracked or torn grid. Cartridges may have a tear or a cut in them, or they are not installed properly and the seal is not tight, so water can bypass the cartridge. Sand filters may have broken laterals (which would allow sand to blow into the pool), or they are fouled to a point where water forces its way around the sand. This condition is called channeling.
Filter channeling creates a cloudy water highway, effectively allowing particles to bypass the filter instead of being captured and removed from circulation. If you have a sand filter, note the pressure and water clarity. If something seems off, it is worth shutting the system off and looking inside the filter for evidence of channeling.1
Channeling is sometimes caused by calcification of some kind, or, more often than not, it's caused by non-living organics and oils fouling the filter media.
Non-living organics such as body waste, tannins, tree sap, dirt, and decomposing plant material waste contribute to chlorine demand and cloudy water. These are just some examples of natural organics. Synthetic bather products, like lotions, deodorants, cosmetics, tanning oils, and sunscreen, also contain non-living organic compounds that contribute to cloudy pool water.
These synthetic compounds are more complex and chlorine struggles to fully oxidize them, resulting in cloudiness and difficulty holding free chlorine. To effectively manage organic waste and maintain water clarity, we supplement chlorine with oxidants using enzymes and secondary oxidation systems like ozone or AOP as part of proactive pool care.
Related: Non-living organics and carbon management (Pillar 2)
All sorts of problems can occur without free chlorine, like algae growth. This is usually accompanied by a green, yellow, or brown color to the water.
Sanitization in water is a battle between the killing rate of the sanitizer (usually chlorine) and the growth and reproduction rate of the contaminant (in this example, algae). According to Robert Lowry, the algae species that can survive in swimming pools can reproduce every 3-6 hours in ideal conditions for them.2
We talk about algae more extensively in other articles and in Orenda Academy™ Four Pillars:
When chlorine is overstabilized with too much cyanuric acid, or bogged down in 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 algae outbreak and eventually cloudy water too. Chlorine is the best algaecide on the market (by far), but even chlorine cannot do everything on its own.
Our strategy for algae prevention is simple:
Water balance is about physics—specifically, the physical saturation equilibrium of calcium carbonate (CaCO3). The best-known metric for quantifying this equilibrium is the Langelier Saturation Index (LSI).
When water is cloudy due to an imbalance, it is because calcium is precipitating out of the water in some form. Typically, this means that calcium carbonate is clouding the water and will eventually turn into dust or hardened scale along surfaces and the waterline. This type of clouding will always be pure white, or gray.
Carbonate clouding can occur for several reasons that raise the LSI abruptly, like:
These products increase the LSI in the immediate area where they are poured. Both soda ash and cal hypo have a pH high enough to convert calcium bicarbonate into calcium carbonate, creating a white cloud. Cal Hypo also introduces a high calcium concentration, making this reaction even more likely.
Related: Why does soda ash cloud pools?
But sometimes, carbonate clouding can occur slowly over time. In these cases, we have found the usual cause is too much carbonate alkalinity, which drives the pH ceiling higher than desired. As the pH naturally rises throughout the week (due to off-gassing carbon dioxide), the LSI will work its way up into a scale-forming condition (above +0.30).
When the LSI rises above +0.30, the water becomes oversaturated with calcium carbonate. Water cannot hold anymore, so it releases the calcium carbonate from solution to bring its saturation back down into an acceptable equilibrium. Water will always return to its natural state.
In the last section, we just covered how adding calcium hypochlorite (cal hypo chlorine), soda ash, sodium bicarbonate, and calcium chloride too quickly can create a high-LSI violation, clouding the water. Now let's look at a few other products and chemical conflicts that can cloud water.
Phosphate removers like PR-10,000 bind with phosphates in the water to create an insoluble white dust that precipitates out of the water. This dust clouds the water temporarily until the dust is either captured in the pool filter or lands on the floor to be vacuumed out.
Related: PR-10,000 frequently asked questions (Orenda Help Center)
The severity of cloudiness depends on phosphate levels and the amount of phosphate remover used. If water is still cloudy after about 24 hours, it could be because oils and organics are in the water (they float) and are sticking to the phosphate dust particles (they sink). If they stick together, the dust and oils stay suspended for much longer. Learn more here.
Not all pool chemicals are compatible. Many of them will conflict with one another in a swimming pool, and some of these conflicts lead to cloudy water. Of note, all non-chlorine algaecide products will eventually conflict with chlorine in one way or another. Each of these algaecide products complicates pool chemistry and increases chlorine demand. This can lead to cloudy water.
Polymer (or polyacrylamide) products also conflict with chlorine. Think poly / polyquat algaecides and polymer clarifiers. The more visible conflict reaction, however, is enzymes vs. polymers. CV-600 and polyquat algaecide will create a lot of bubbles and turbidity for up to a couple of days. The severity and length of time of the cloudiness depends on circulation, filtration, and water temperature.
Other conflicts may occur, especially if non-chlorine sanitizers like biguanides and hydrogen peroxide are used. But those pools have fundamentally different chemistry to begin with.
Contrary to popular belief, total dissolved solids (TDS) do not directly contribute to cloudy water. TDS is a measure of all the dissolved solids in the water, meaning they are in solution and invisible to the naked eye. Cloudy water is created by suspended solids, not dissolved solids.
That being said, TDS is a decent proxy of other factors that could lead to cloudy water. Namely higher levels of calcium hardness, total alkalinity and cyanuric acid. All three factors impact the LSI, and CYA directly impacts water quality too.
We have seen no compelling evidence in the field or in research papers that indicates TDS is directly correlated with cloudy water. It's just commonly assumed so.
Any pool can have world-class water clarity. Why not yours?
Cloudy water can happen for a number of reasons, spanning across water quality, water balance, and pool products used. Turbidity (the fancy word for cloudiness) looks different in each case.
For a water quality issue, the cloudiness will have an earthy color to it (green, yellow or brownish tint). For a water balance issue, it's usually calcium carbonate coming out of solution, which is pure white, which may also appear gray. Product conflicts are usually temporary, and they will often be accompanied by other reactions like foaming and films on the water.
Our recommendations to prevent and clean up cloudy water are the same:
If you have cloudy water and this article does not explain your situation, please reach out through our help center.
1 Always follow the filter manufacturer's instructions. Opening filters can be extremely dangerous, so it's best to leave this process to a trained pool professional. Always shut off circulation and appropriate valves as needed for your pool. Every pool system is slightly different.
2 Lowry, Robert W. (2016) IPSSA Basic Training Manual, 2016 revised edition.