Langelier Saturation Index Inaccuracies

The Langelier Saturation Index is the basis of swimming pool water chemistry. A simple mathematical formula determines whether the water is in balance (neither corrosive nor scale forming). Realistically, not a measure of the success in preventing algae or bacteria, but a calculation designed specifically for the protection of the vessel, the swimming pool itself—a determination of calcium carbonate saturation. Let’s face it; we have come to depend upon the accuracy of the pool industry LSI (Langelier Saturation Index).

The water being in balance is extremely important, and the LSI is a tool we rely upon. After all, we know water needs to have a certain amount of calcium and carbonate in solution, and the level we need varies upon both temperature and pH. If the water is found to be corrosive, it will pull calcium and carbonate from the pool walls and floor, etching the surface. When the water is scale forming, everything from a cloudy water condition to calcium carbonate deposits forming about the pool.

This Photo by Unknown Author is licensed under CC BY

Many think calcium carbonate saturation is only important in plaster pools, and that’s not the case. Nowadays, liner companies utilize calcium carbonate in the production of vinyl. The amount used varies from manufacturer to manufacturer, but it has been found that corrosive water can pull calcium carbonate from vinyl when the content is greater than 7%. It is also a fact that cobalt staining is more prevalent in fiberglass pools where a corrosive saturation index persists.

Dr. Wilfred Langelier, professor emeritus of civil engineering at the University of California, Berkeley published this concept in a paper titled The analytical control of anti-corrosion water treatment in 1936 in the detailing the model was first published in 1936 in the Journal of the American Water Works Association. Most are aware of this; however, a common misconception is that we actually use Dr. Langelier’s model, which was designed to determine the Potential for calcium carbonate precipitation. In actuality, we do not.

A Mother of a Math Problem

Langelier’s formula, despite its accuracy, is extremely complex. It also was not designed to determine whether water was corrosive or scale forming. Instead, as I mentioned above, the calculation only determined the calcium carbonate precipitation potential (CCPP). Not a guarantee that a problem with calcium would occur, only a predictive measure of an increased possibility. Regardless, Langelier (already widely known for his advances in water treatment due to studies documented in his 1921 paper Coagulation of Water with Alum by Prolonged Agitation) came up with a highly complex formula. That was beyond practical for longhand calculation – the math was insane!

View the entire Journal of the American Water Works Association 1936-10, Vol 28 HERE

Due to its complexity and advances in science, the formula was simplified in 1965 by Carrier (heating, air-conditioning, and refrigeration solutions). This new version is often referred to as the ‘improved’ version and was the first to call the formula the Langelier Saturation Index. Oh yeah, I almost forgot – pHs is the name Langelier gave to his formula for predicting calcium carbonate precipitation potential.

Is Carrier’s LSI improved? Answering that question is beyond my skill set, but I can say it definitely dumbed it down. With that, of course, some suggest this revised 1965 method is too simplistic to be as accurate. However, this new calculation is more similar to the formula that we use now in the swimming pool industry. That’s right; we’re not up to what we use for swimming pools just yet. That doesn’t happen until 1974.

Change is good, right?

This was when John A. Wojtowicz of Chemcon got his hands on it. Wojtowicz pointed out that the LSI in its current version did not consider other alkaline substances that would contribute to the Total Alkalinity in a swimming pool (i.e., cyanuric acid, boric acid, etc.). So, the formula was retooled once again. See The Effect of Cyanuric Acid and
Other Interferences on Carbonate Alkalinity Measurement
in the Journal of the Swimming Pool and Spa Industry

This is where we are at now – the Wojtowicz Saturation Index? Not sure if this name will stick, but it is certainly more accurate than calling is LSI. Misnomer or not, this is the saturation index calculation that we use in the pool industry today. This is where the formula for the LSI apps we use originated. Accuracy in attribution or not, is it more accurate in predicting the potential for calcium carbonate to precipitate in an open body of water?

Crystal structure of Calcite By Materialscientist at English Wikipedia, CC BY-SA 3.0,

I thought it would be interesting to see the difference in calculation between the three using values we would likely see in a swimming pool, specifically omitting the presence of cyanuric acid, borate, or any other substances that might affect our Total Alkalinity.

Our example water test:

Water Temperature


Calcium Hardness

Total Alkalinity

Cyanuric acid



Total Dissolved Solids

81° F


300 ppm

90 ppm

0 ppm

0 ppm

0 ppm

1,000 ppm

Saturation Results:


1936 – Dr. Wilfred Langelier – pHs

1965 – Carrier – LSI

1974 – Wojtowicz – Pool Industry LSI (using a currently popular industry app)

Index Calculation







Supersaturated – Scaling possible

Scale forming and corrosive

In Balance – not scale forming, not corrosive.

A Formula never intended to be used in an open body of water exposed to atmospheric pressure 🤷‍♂️

Another factor to consider – The saturation index is said to only be accurate within certain parameters. Luckily, the chemistry we keep in swimming pools typically falls within that range. That is except for Saltwater pools.

  • pH: 6.5 to 9.5
  • Temperature: 32 to 212°F
  • Bicarbonate alkalinity: 10 to 800 ppm
  • Calcium hardness: 50 to 700 ppm (up to 900 ppm)
  • Total dissolved solids: 50 to 1000

Accuracy of the pool industry LSI

If Dr. Langelier’s pHs is the more accurate measure of determining the water’s potential of calcium carbonate precipitation and was truly only changed for ease of calculation, with the capabilities of cell phones, wouldn’t it make more sense to develop an app that could quickly perform the complex equation? Of course, Wojtowicz’s Carbonate Alkalinity would be a necessary modification in a swimming pool application.

If not, and today’s LSI method continues to be the route we take, do we really need an app or studies on mathematical calculations at all? I mean, the reality of it is shooting for the dead center of the ideal range on the three values for which an ideal range exists; the water will always be in LSI balance down to a temperature of 48°F and as high as 104°F anyway. The exception being a saltwater pool in which none of the calculations are apparently accurate anyway.

Specific Parameters

Even if the inaccuracy of the LSI at a Total Dissolved Solids (TDS) level above 1,000 ppm did not exist, maintaining a pH of 7.5, Carbonate Alkalinity of 90 ppm, and a Calcium Hardness of 300 ppm would keep the water balanced on today’s pool industry LSI balanced in water temp range of 63°F to well over 104 degrees (TDS of 3,000 ppm).

Have an LSI app on your phone? Try it! Set the pH at 7.5, Carbonate Alkalinity at 90 ppm, and the Calcium Hardness at 300 ppm. Now play around with different numbers for temperature and TDS. Do we really need an app? Or, would a simple dosing calculator suffice?

Simon Says No To CyA!

Subject: A Topic Idea for Pool Operator Talk News  

The following represents the thoughts of a dedicated Pool Operator Talk News reader and do not necessarily reflect the opinions or viewpoint of Pool Operator Talk News. Simon Spragg of Tech Pools Costa Blanca, Spain.

Simon Spragg of Tech Pools Costa Blanca, Spain.

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Having read your posts on CyA/chlorine lock, I have some data from this summer that may be beneficial—agreeing with Ben and Robert re CYA effect. The more CYA, the worse the water becomes (for more reasons than chlorine inefficiency). So adjust water to 30ppm (Taylor turbidity test

With water at its max temperature in summer (30°c), add a minimum of 10% (sodium hypochlorite) to CYA = 3ppm at 20.00 every 24 hours (use a programmable peristaltic pump).

For heavy bather use (holiday renters families etc.) add 4ppm (or as necessary. Test Taylor FAS / DPD, at midday, aiming for 1.5-2ppm)
Maintain pH at 7.2-7.4 (again use peristaltic pump add in advance of chlorine injection)

Calculate pH demand using the Taylor acid demand test and work out % of acid to chlorine (typically between 15-25%). To keep the water balanced and non-corrosive, adjust LSI to be positive of zero (Orenda tech app is most natural or Taylor water wheel). The answer or key here is calcium at 350/400 ppm, then TA at approx 90. Cal at these levels creates more excellent stability.

This creates sparkling algae-free pools. Add UV and varispeed pump (running 24/7), then the contaminants get better filtered, and you know bacteria/virus, etc., are continually being destroyed… Adding FC at night (sodium hypo) means no sun effect and at a level way above CYA demand = effective Oxidation.

Simon Spragg of Tech Pools Costa Blanca, Spain

Understanding pH demand ensures clarity.

Keeping LSI just positive makes comfortable non-corrosive water. The industry is best advised to find a way of banning the manufacture of “so-called chlorine tablets.” Tablet abuse.

Manufacturers have worked out CYA/chlorine inefficiency. This is why the trichlor chemistry includes additives such as copper sulfate (to kill algae) and aluminum sulfate to coagulate algae. Therefore ease of use and a clear looking pool (until the end of summer). For the DIY bod and low-value pool cleaners, they can measure high chlorine levels from small quantities of tabs = more profit.

But the trade-off is rubbish quality water unsafe water, corrosive water, un warrantied pump heaters, etc. The problem is pool shops and supermarkets who frankly don’t care or know this stuff, and they want the bottom line in cash.

Look forward to hearing your comments

Pentair R151226 79 Cyanuric Acid Test Kit

Why Test my Pool for Calcium Hardness ❔

By Eric Knight

The Benefits of Calcium Hardness in Cold Water ?

Calcium is often treated like a four-letter-word by pool service professionals. This negative opinion of calcium comes from a misunderstanding, equating high levels of calcium hardness to carbonate scale. This article will not only debunk that opinion but make a case for maintaining higher, healthier levels of calcium hardness in your swimming pool. It’s a proactive thing to do, especially in the winter. The Benefits of Calcium Hardness in Cold Water!

Eric Knight, Orenda Technologies

Let’s begin with the fundamental misunderstanding about calcium hardness. Most of us think that high calcium hardness is the primary cause of scale formation…but that’s not accurate. This is confusing because the Langelier Saturation Index (LSI) measures the saturation equilibrium of calcium carbonate (CaCO3). It only makes sense to think of calcium hardness as the cause of that hardened calcium deposit in the salt chlorine generator, heat exchanger, or on the tile line. Calcium scale MUST be because of high calcium, right?

It’s the pH in water balance

Not necessarily. Sure, calcium is obviously a factor, but not the primary factor that drives scale formation. When we look at the LSI, we see that calcium hardness is far less impactful than pH. Alkalinity, too, has a stronger impact on the LSI than calcium hardness. Water temperature also plays a role, whereby each ºF moves the LSI by 0.01. Calcium Hardness Water Balance

Calcium as Insulation

While calcium’s impact on scale formation is significantly less than pH–and to a lesser extent, alkalinity–calcium brings a few undeniable advantages when it comes to water chemistry. First, if the name of the game is maintaining LSI balance, nothing comes close to calcium in terms of reliability and consistency. Calcium is remarkably stable. If you have 250 ppm in April, you will probably have close to 250 ppm in August (unless you are using Cal Hypo as primary chlorine). Contrast that with pH, which might as well be a rabbit jumping up and down, or alkalinity, which also moves up and down.

Calcium dissolves better in cold water

The second advantage of calcium is its solubility in cold water. In climates where swimming pools are winterized or even those that dip down into the 50º area, calcium hardness becomes vital. Almost every substance dissolves easier in hot water, but not calcium. Calcium dissolves easier in cold water. So when the water temperature drops, you can count on calcium hardness to be there…just make sure you have enough of it. The biggest mistake we see in winterization is ignorance of the LSI. And the most reliable way to maintain LSI balance in cold water is with calcium hardness. We think of it sort of like insulation, or food for the bear (pool) about to hibernate (winterization). Can we rely on alkalinity or pH to stay the same during the winter months?

Etching vs. Scale

The LSI is the unbiased indicator of water balance. On the low end (< -0.30), water is aggressive and hungry for more calcium carbonate. This aggressive water is what causes etching in cementitious pools. In vinyl or fiberglass pools, it causes fading. Etching and fading are permanent damage.

The flip side is a high LSI (> +0.30), which means the water is over-saturated with calcium carbonate…it has too much. Since water cannot be greedy, it must deposit this excess calcium carbonate somewhere, and water temperature usually indicates where. This is why hot salt chlorine generators and heat exchangers tend to scale up first, then a sunny tile line or spillway. This also explains why your shower head at home may have scale on it, but the bathtub itself probably does not.

The Significant Six ?‍♂️

There are six factors to the LSI, and they all matter. The bad news is, it’s 6 factors to keep track of and manage. The good news is there are plenty of options on how to manage water chemistry and to overcome out-of-range chemistries. For instance, extremely high calcium hardness (800 ppm+) does not have to cause scale, if you keep your pH at 7.2 and alkalinity at 80. And an 8.0 pH does not necessarily cause scale either if you have CYA over 80 in a salt pool with 4000 TDS. Play around with the free Orenda App, and you will see how the factors can be used to your advantage.

All you need to focus on is getting the LSI value to be a green number. There are 720 combinations to do it (the factorial of 6).

flikr user fdecomite

Calcium as a Foundation

We like to build our water chemistry strategy on a foundation of calcium hardness. Why? Because it is so stable and reliable. The ideal calcium hardness level is whatever allows you to quickly balance the LSI year-round. Maybe in sunny south Florida, that’s 250 ppm. In cold Minnesota, it’s probably more like 450 – 500 ppm. If your pool freezes, in Orenda’s opinion, 400 ppm is the bare minimum for the winter.

With a solid foundation of calcium year-round, you might find that maintaining LSI balance becomes a lot easier and more affordable. Instead of pursuing a moving pH, you can make micro-adjustments and keep them in line. With salt or liquid chlorine, the pH climb is predictable, and therefore controllable. Without a foundation of calcium hardness, the range of movement is more significant, and therefore more difficult (and expensive) to manage.

Calcium is your best friend.

Similar Article What is Total Dissolved Solids?

Pool Management Apps

The Dirty Swimming Pool Water Epidemic Includes Your Pool – Yes, Yours!

It’s the week before Memorial Day 2018 and the Center For Disease Control releases its latest findings on pool and spas for Healthy and Safe Swimming Week.  The title reads “1 in 3 Swimming-Related Disease Outbreaks Occur at Hotels” and is picked up by just about every News agency and local paper during the following month.

If you own or manage a hotel, motel or vacation resort, this is probably NOT how you envisioned the kickoff to your summer season! Your guests are now inspecting your pool and second guessing whether they should jump in.

No worries, you have trained staff that clean and balance the water chemicals in your pool daily, or hourly, according to health department regulations. It’s one of their many jobs.

The Oh Cr@P Moment
Surprise! Your state health inspector has stopped in for a visit during prime sunbathing time and closes down your pool for the day. Apparently, your staff forgot to test the pool this morning and hasn’t been entering the data into the pool chemical log.  I guess you should have gone down to the pool and reviewed the logs, but you were busy too.

Luckily you got off easy, for now. Just a small fine, and some grumbling guests, with crying kids, who can’t use the pool for 24 hours claiming you ruined their vacation.


Lets just hope no one reads the reviews that get posted this morning, and no one gets sick and blames it on your pool since you now have no proof they are wrong!

80 % of commercial pools have health code violations, typically due to incorrect chemicals or record keeping.  12% are shut down immediately upon inspection according to the CDC report from 2013.

This is nothing new, these statistics haven’t changed in the past 5+ years.

The World Has Gone Digital. Take Advantage NOW!
What if your company and staff could benefit from the digital revolution? Almost everyone has a smartphone in their pocket that can be used for everything from reading to shopping and now POOL MAINTENANCE!

Pool Shark H2O is an electronic pool maintenance system providing online pool chemical logs, instant water analysis and dosage calculation for all your pools and staff.  Eliminating paper handling and time spent calculating chemical dosages is cost effective and keeps the pool water safe for guests.  Pool Shark H2O is 100% compliant with health department regulations and works on Windows, Android and Apple devices.

As a manager, you no longer need to walk around your facilities to check the pool logs as they are all available instantly from your desk or smartphone.  Even better, you are notified by the Pool Shark H2O system when a pool hasn’t been tested or if the water chemicals are incorrect. Weekly reports are automatically emailed to you to ensure accountability from your staff.

Listen to Pool Talk interview with Pool Shark H20 CEO Scott Trafton: Pool Talk

Pool Shark H2O
While the story above is somewhat fictional, the statistics are real. It is based on what we commonly hear from clients, many of whom are commercial pool owners and Certified Pool Operators looking for a faster way to maintain pools, or regional property managers with facilities spanning the United States and Canada.

If you or your company are looking for an easier way to keep pools and spas clean that complies with your local health departments regulations, give us a try.

Visit for a 30 day trial.

Use Promo Code: SHARK2018 and they’ll take 10% off your first year’s paid subscription.


Raising pH with Air

Spas, Splash pads, and Waterpark rides…

Ever wonder why the pH tends to run high in certain bodies of water no matter what you do? Always adding acid? Spas, Splash pads, swimming pools with water features, and literally everything at a waterpark. They all have one thing in common.


When water is aerated, it creates turbulence. The turbulence then causes the aqueous CO2 (carbon dioxide) to outgas. Outgassing of COfrom water results in an increase in pH. Aeration is the only means of increasing pH that will not increase the Total Alkalinity. This is both beneficial and problematic.

At Aquatic Facility Training & Consultants, we think it’s important to know the “why” behind things. To understand the reason for the increased consumption of acid at these facilities. If you can embrace the science in what we do, swimming pools become increasingly easy to care for.

My pool, at my house; the pH always runs on the low side. My yard has long leaf pine. Pine needles, when green, are acidic. Even if they do not fall directly into the pool, when the needles get wet, they drip. This drives the pH down. My pH, left to its own, would be a consistant 7.0

Four years ago, with the knowledge of aeration, I decided I would run an experiment. I took a single return jet (where the water comes back into the pool through the wall) and loosened the collar. I aimed the jet toward the surface so that it would cause that ripple in the water. Within three days, the pH in my 15′ x 30′ rose to 7.6. Between the turbulence caused by the jet and the acidity from the pine needles above, my pH has remained between 7.5 and 7.6 for the past four years without the need to add a chemical for adustment; up or down. Wouldn’t it be great if you could harness this power and not have to worry about a pH too low?

What about that pool you have on your service route where the pH always runs high (saltwater pools excluded)? Maybe it doesn’t have a water feature. Next time you are there, take a look at where the return jets are aimed. A lot of times home owners will aim their jets upward, because “they like to see the water move… Your real problem is not the pool. You have been fighting science and losing the battle against aeration.  Loosen the collars and aim those jets back downward – pH problem solved.

Many times, during the summer months, competition pools utilize water cannons to cool the water temps. These cannons shoot water through the air in an effort to keep the water within the USA Swimming guidelines for competition (between 25 to 28 degrees Celsius (77 to 82.4 degrees Fahrenheit)). This can be a double edged sword. The cannons are very effective at reducing water temperature. However, they do create a ?-ton of turbulence. This drives the pH upward, but remember earlier I had mentioned that aeration would not raise the Total Alkalinity? This is a problem.

So if the aeration created by the water cannons causes the pH to rise, we will need to add acid to lower it. Makes perfect sense, right? Here’s the thing: it is impossible to add acid to lower the pH without it also lowering the Total Alkalinity. But, again, the turbulence did not raise the Total Alkalinity; just the pH. That means that our continuous feed of muriatic acid necessary to counter balance the aeration of the cannons and keep the pH in check has driven our Total Alkalinity to a level too low. It is not uncommon to see that some type of sodium bicarb feed system has been added to these pools to counter the dose of acid.

An alternative at competition pools to muriatic acid is the injection of carbon dioxide (CO2). When COis added to water if forms carbonic acid (H2CO3) Carbonic acid is very effective at lowering pH. Unfortunately, injecting COto form carbonic acid (H2CO3) is the only method of lowering pH that will also increase the Total Alkalinity. Ultimately, the pool would then require the addition of muriatic acid.

I don’t want to delve deeply into the MYTH at this point in time because more information is coming in the near future. Still, we need to understand that it is impossible to add acid to lower the Total Alkalinity without lowering the pH, and vice versa. Many have said in the past, and many still believe, that the method of introduction of acid to water will enable a person to lower one without affecting the other. This is simply untrue.

pH stands for potenz Hydrogen, which translates from German to “the power of Hydrogen” Anytime acid is added to water it increases the Hydrogen ion level. If you add acid to water in order to lower the Total Alkalinity (as our CO2 method above would eventually require), the Hydrogen Ion level will increase. As pH is the measurement of the water’s demand for acid (more specifically, hydrogen activity measured in the converse), the pH would lessen; a low pH indicating a low demand. In short, if you increase the amount of Hydrogen Ions while lowering the TA, does it not make sense that you will affect a reading that measures Hydrogen ion concentration in that soultion (the power of Hydrogen (pH)) ??? The same holds true when the levels are increased (Yet another entirely different conversation), with exception to aeration. This leaves aeration the only method of altering pH with an effect something else, or does it? What would be the impact of aeration on water temperature as noted with the water cannons above?

One Pound of Anything Dissolved in 10,000 gallons Will Increase Total Dissolved Solids by 12 ppm

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 ?Total Dissolved Solids


Anything you add to a pool will increase something, and everything will increase TDS. For example, a gallon of sodium hypochlorite (containing 2.34 pounds of solids) will add 12 ppm of FAC (Free Available Chlorine) to 10,000 gallons of water and will increase the TDS by 28 ppm. 15 oz. of trichlor (stabilized chlorine tablets/granular) will add 10 ppm of FAC to 10,000g, but it will also increase the CYA (Cyanuric Acid) by 6 ppm and the TDS by 10 ppm. Calhypo (Calcium Hypochlorite) added at a rate of 20 oz. Per 10,000g will add 10 ppm of FAC, but will also increase your Water Hardness by 8 ppm and your Total Dissolved Solids by 15 ppm. Even a cup of muriatic acid (containing 1.87 pounds of solids per gallon) will raise the TDS by 1.4 ppm. What is Total Dissolved Solids?

“The Age of the Water.”

Take into consideration that the water straight from the tap, even before you add anything, has a level of Total Dissolved Solids. It is essential in swimming pool maintenance that we know what that starting level is. The TDS level is not something that will decline over time – it only increases. The only means we have to lower the level of dissolved solids is to replace water. We should drain and refill the pool when the TDS increases by 1500ppm over what we started with, at least partially.

“Dilution is the Solution to Pollution”


Evaporation is also going to be a factor in an ever-increasing Total Dissolved Solids level. When water evaporates, the only thing that leaves the swimming pool is water. The solids that were present in the evaporative loss are left behind. This increases the total in the water that remains. Then, the replacement water only adds additional solids to the solution.

TDS meter.

These electronic testers vary in price, from less than $100 to well over $1,000. The meter serves as an indirect means of determining the level. What this measures is the electrical conductivity (EC) of a solution; this occurs by sending a charge between the two electrodes of the device. Ionized particles such as salts and minerals increase the EC; because of this, our results can be misleading.

Not all solids dissolved in water are ionized. However, they do still contribute to the TDS level. Take the sugar added to a cup of coffee, for example, though dissolved and a contributor to Total Dissolved Solids; it is undetected by our TDS/EC meter.

Galvanic Corrosion

GC (galvanic corrosion) can be recognized when metal components (light rings, handrails, ladders) submersed in water turn black. This is usually an indication of a high TDS, but the Total Dissolved Solids itself is only a contributing factor and not the actual cause. As NACE International explains it: “Galvanic corrosion (also called “dissimilar metal corrosion” or wrongly “electrolysis”) refers to corrosion damage induced when two dissimilar materials couple in a corrosive-electrolyte.

Galvanic Corrosion
Purchase a TDS meter?

The Total Dissolved Solids level in a swimming pool can take years before it increases by 1500 ppm over your starting value, so you could bring a water sample to the pool store and have it tested quarterly. What about the Saturation Index you learned about in CPO® Certification Class?

Similar Article The Truth About Saltwater Pools ?

Because your factor for TDS is either 12.1 or 12.2 (NSPF Guidelines), you could honestly guess for this calculation; if you were to shoot for an LSI of 0, in a worst-case scenario, you would only be off by ).01 in either direction. With a balanced range of -0.03 to +0.03, you would still hit the mark.  A spa, however, is an entirely different story, and I would say that those who maintain one should own a TDS meter. In a small hot water environment, the Total Dissolved Solids level can increase by that amount in a matter of weeks, or even in days (depending upon bather load/usage).