This blog post is a summary of a Webinar co-hosted by Niki Acosta and Eric Knight. Watch the full webinar on demand here.
“Water is not dictated by mankind. It never was, and it never will be. It’s controlled by laws of nature.” This is how Orenda’s Eric Knight opened up our recent webinar. It’s also the main principle on which the The Langelier Saturation Index (LSI) was built.
Specifically, the laws of nature dictate that, no matter what, water will always return to its natural state. This is why pool pros exist, but it’s also why they continue to be frustrated in their day-to-day activities. At times, pool service can feel like fighting against nature. But understanding the LSI is a big part of changing pool pros’ relationships to water chemistry.
During this webinar, Eric went in-depth on how to understand LSI: what it is, how to master it, and how to use its principles to save time, save money, and prevent common issues. Below is a recap of what was covered, plus a summary of answers to an especially lively Q&A period.
What is LSI?
Dr. Wilfred Langelier created LSI in 1936 to protect drinking water infrastructure from corrosion. Since then, it has been used to determine the saturation equilibrium of calcium carbonate (though it’s since been adapted for pool chemistry).
Understanding the LSI changes the way pool pros approach both water quality and water physics. On the water quality side, the fact that water will always return to its natural state means that if you abandon your pool, it will end up looking like a pond or a swamp.
On the water balance side, it all comes down to physics. Pool pros can either comply with the physics that govern pools or get in their way. Swimming pool physics are made up of two components:
- Water physics, which is quantified by LSI
- Air physics, which is dictated by Henry’s Law (and states that the air is going to equalize with gas as it’s dissolved into the pool)
If we understand swimming pool physics, we can prevent things like:
- Calcium flakes in salt pools
- Scale in heaters and spas
- Corrosion in heaters
If you want to be profitable in pools, you need to ensure that your water is predictable. And the only way to have predictable water is by understanding its physics.
In the pool service trade, people get frustrated. Pool pros do the same thing week after week but feel like the water keeps changing. Eric points out that we’re the variable, not the water. Water will do the same thing, the same way, every time. Once we start to understand that, we can change the way we interact with it.
Water physics: Mastering the LSI
At a high level, LSI answers the question, “What level of saturation of calcium do I have right now, at my current pH, temperature, TDS, alkalinity, CA, and borate (if used)?” We need to group these factors together because water doesn’t care about any of them individually. It cares about all of them together.
To visualize why calcium carbonate saturation matters, think about adding sugar to a glass of water (in this example, sugar is a stand-in for calcium carbonate). As you add more sugar to the glass, it will dissolve—until it doesn’t. Once it hits a saturation point, any more sugar that’s added will sink to the bottom of the glass. With pools, oversaturation of calcium carbonate shows up as scale or calcium flakes.
LSI shows you where water is going
Pools have a perfect equilibrium of calcium carbonate at 0.0. But you can be anywhere between 0.3 and -0.3 and still have an acceptable saturation level.
More than anything, using the LSI lets pool pros understand where their pool’s water balance is going. And just like a quarterback throws a football to where a wide receiver is going, pools should be treated based on where the water is going.
Water cares deeply about calcium saturation. When it gets thrown off, you run into problems. For example, having scale means you have too much calcium carbonate saturation in the current conditions of your water (and it will always show up in the highest-LSI places first).
When in doubt, just follow the colors
If reading all that gave you a headache, fear not: this is why the LSI calculator exists. If you have the Skimmer app, you just need to follow the colors in the LSI calculator. They tell you whether you have an under or over-saturation of calcium carbonate.
Your one job is to stay yellow or green in the LSI calculator year-round. When you see a purple number, the water is oversaturated. You're likely to have a scale-forming condition in the near future. When you see a red number, the water is undersaturated and starved for calcium carbonate.
Containing pH
Air physics tells us where the pH is going. The key is having a contained pH with LSI balanced when it gets to the ceiling. Your water is headed towards its pH ceiling no matter what, so you want to make sure it will be balanced when it gets there.
Henry’s Law states that any gas dissolved in a liquid has to equalize with the gas above the liquid. The amount of CO2 in our water determines the pH.
More dissolved CO2 means a lower pH. As you lose CO2, the pH goes up. CO2 naturally off-gases, meaning that pH naturally rises. If you use auto covers, you’ve probably noticed that after a week, the pH is not quite as high as pools that don’t use them. If your pool can’t respirate, it can’t lose CO2.
The good news? This is all in your Skimmer app. If you want to know how high your pH can naturally rise, just plug in all your values. The calculator does the math for you and automatically corrects.
You want to work with pool physics so that you’re LSI balanced when your pH rises to its ceiling. You can let pH rise up to its ceiling naturally during the week, then reset it to a yellow LSI level (usually 7.6). This strategy can’t fail you as long as you’re putting in accurate information.
Precision dosing
Question: How much Muriatic Acid does it take to lower the pH of a 20,000 gallon pool from 8.0 to 7.5?
The answer depends on your total alkalinity. The lower your alkalinity, the lower your acid dose. If you have 100 alkalinity, your acid dose is under a quart. If you only have 60 alkalinity, you have 3x the acid dose and you drop your pH to the low 5’s. That’s a huge LSI violation. You can’t just build a habit around how much Muriatic Acid a pool needs. Use the calculator. It will correctly lead you to a very precise dose, every time, assuming you know the volume of the pool.
You also want to make sure you dilute it (at a minimum ratio of 10:1), or it will go straight to the bottom every time. The correct order of operations for adding Muriatic Acid is:
- Dose correctly using the calculator
- Measure
- Dilute
- Pour it in the pool
You want the acid to matriculate slowly and find the alkalinity so that by the time it gets to the bottom, it’s not acid anymore.
Prevention of common issues
Many common issues that show up in pools are the result of LSI violations. Eric went through some examples, and shared how to fix each one.
Calcium flakes in saltwater pools
Calcium flakes show up when there’s an LSI violation within the salt cell. Contrary to popular belief, this is not caused by a failure of the salt cell itself. It usually means there’s too much total alkalinity (TA) in the water and too high of an LSI.
If you understand what a salt cell is doing, calcium flakes are easy to prevent. A salt system is regenerating chloride ions using electricity. Inside the cell, there’s a high pH on the cathode and a low pH chlorine gas on the anode.
When the electricity shifts directions, the high pH could have had calcium on it. The acid fractures that off and it blows in as flakes. Afterward, they neutralize. The other byproduct is hydrogen gas, which is not soluble and creates turbulence. That turbulence forces CO2 out, which raises the pH.
Tip: If you have a salt cell on a pool with an autocover, it can destroy that pool because the CO2 has nowhere to go and goes after your surface. You have to off-gas CO2. When the cover is closed, the cell should not fire.
Two actions prevent calcium flakes:
- Get your pH ceiling to 8.09 or less on the calculator. You can’t do that if your alkalinity is over 65 in the summertime. You want to be at a total alkalinity of between 60-65, and your LSI should be balanced when it gets to that pH ceiling.
- Chelate your calcium. This binds the calcium so it cannot bind to a carbonate or phosphate. It keeps it in solution, which stops these problems within a week.
Scale in heat exchangers
This happens when your pH ceiling is too high. It’s forcing an LSI violation within the heater (it’s hot in there!). Scale forms over time. Like salt cell scale, TA in the water is too high relative to calcium hardness, and too high of an LSI. Scale does not damage heaters, but it does reduce their efficiency and increases pressure. Enough scale can cause problems.
To fix it, as in the previous example, you want to chelate your calcium and get your pH ceiling to 8.09 or less.
Corrosion in heat exchangers
Corrosion can happen for many reasons. It’s not just a low LSI, although that’s a likely reason. If you have a low LSI, you have parameters that are corrosive. It could be caused by any of the following:
- A low pH
- High sulfates
- High chlorides
To prevent this, follow these three rules:
- No tabs in skimmers
- No column pouring acid
- No overdosing acid or not diluting it
Using the Orenda LSI Calculator in the Skimmer app
In Skimmer, the LSI calculator is the same as what you’d see in the Orenda app. The only difference is that the Skimmer app puts that calculation within the context of your workflow. It also gives you an LSI history and a context record.
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When you click “Get Dosages” in the calculator, you’ll see a series of actions to take as you’re servicing the pool to get to LSI balance. Overall, we can’t tell you where your desired readings should go. A pool in Miami has different parameters than a pool in Michigan. We can only tell you how to get to LSI balance, and it’s up to you to know what’s best for your business.
One of the main benefits of using the LSI calculator within the Skimmer app is that it gives you a historical trend to refer back to, which isn’t available in the Orenda app. By referring to this trend over time, you’ll eventually realize how much less you’re spending. This will allow you to forecast better.
The left side of the calculator is where you test. In this section, you can run tests on factors like Total Alkalinity to see where your pH ceiling will be in a week.
The greatest benefit of using the LSI calculator is that it allows you to obey the two laws of physics. When you do that correctly, you only have to focus on water quality. It’s a much more efficient way to handle pools.
Your FAQs about LSI answered
Q: How do you chelate calcium?
A: Use SC-1000, and follow the dosing. If you need to purge, use 32 ounces—or a quart—per 10,000 gallons. If you’re adding calcium chloride to a pool, it’s one ounce per five pounds. For a 50-pound bag, it’s 10 ounces.
You can also use a sequestering agent, which won’t last as long in sunlight.
Q: What is the best way to test total dissolved solids (TDS) in a non-saltwater pool for a service pro?
A: There are a few digital meters you can use (Eric uses a Lamotte TRACER 1766). There are also test strips that can get you in the ballpark, but they’re not as accurate. TDS includes salt, so use a digital TDS pen and keep it calibrated.
Q: How do you easily measure CYA?
A: There is no easy way, but the most foolproof way is with melamine reagent. If you have CYA in the water, it will cloud. No test is good under 30, but the best way to do it is to know how much you put in. Know your pool volume and get a dose of exactly how much CYA to add. Or use the Orenda Chemiculator and use Dichlor. Things get out of control when you use tabs.
Q: pH TA targets -0.3 to +0.5. Why is Orenda still using the previous threshold?
A: Because they haven’t provided evidence on why they use the 0.5, and there’s no scientific evidence for it. It may be because it’s the highest in the ideal ranges, but it’s not scientifically based. Until we see scientific proof, we won’t be changing it.
Q: How are the Orenda app’s LSI parameters different from how Dr. Wilfred Langelier originally designed LSI?
A: It’s been adapted for pools, and also according to how technology has developed in the last nearly 100 years. There is an article in Orenda’s Help Center that gives the whole story.
Q: Do PoolRx units affect LSI levels?
A: They shouldn’t. PoolRx units are mineral systems. They don’t do much for germs, but they do reduce algae.
Q: Will having an auto-cover affect the buildup on salt cells more?
A: Not directly, but the buildup is a localized LSI violation. You could have that buildup, but the overall pH is suppressed because you can’t get the CO2 out..
What really matters is how carbonated your water is. Where is your pH ceiling? Your ceiling is based on the carbonation level at a current temperature. As the water heats up, that number moves. Calcification happens when your pH ceiling is too high, no matter what.
Q: If a salt cell produced pH-neutral chlorine, why would the pH rise? I was under the impression that chlorine gas had a high pH, which would cause the pH to rise?
A: Chlorine gas is a pure acid. When it dissolves, you get Hypochlorous Acid and Muriatic Acid. Every type of chlorine releases muriatic acid. Once chlorine breaks down, it loses oxygen and releases Muriatic Acid.
Chlorine gas doesn’t have that problem. It dissolves in water and becomes HOCL and HCL (a pure acid). That’s what neutralizes hydroxide. Loss of CO2 raises your pH. In a pH of 7.0, the chlorine gas perfectly neutralizes the hydroxide. The turbulence in the cell raises your pH.
Q: When you say pH always goes up, we find that to not be true with trichlor. Why is that?
A: pH rises up towards its ceiling (its natural state). We all have carbonated pools. When you’re at the pH ceiling, the amount of carbonate in your water is equalized by the air above it. That’s why we call it the ceiling. You can’t lose any more carbonation.
If you had two beers and swirled one, it would go flat faster because of the turbulence. Similarly, salt cells create turbulence. With trichlor, it’s acidic with a 2.8 pH. To create CO2, it burns through alkalinity by adding a hydrogen. It slowly erodes and burns through alkalinity, converting it to CO2. This pushes the pH down at the cost of more alkalinity. That’s why you buy so much bicarbonate with a tab pool.
Q: How would you clear calcium carbonate from the pool surface?
A: If it’s on there, you can follow the “soften and remove scale” process in the Orenda app. Get your pH ceiling below 8.1 and get a chelant in there.
Q: As a commercial operator, how often should you do an LSI test?
A: Some rules of thumb:
- Test your temperature, pH, and chlorine 2 or 3 times a day.
- Test alkalinity once a day or once a week at a minimum.
- Test calcium, CYA, and TDS once a month, because they don’t change much.
Some exceptions: if you’re on Cal Hypo, you do need to know your calcium more frequently (weekly) until you know your rate of consumption. If you’re on trichlor, measure CYA each week to see how fast it’s rising. If you use Skimmer, you can see a trend line.
Q: In pools where you use liquid chlorine, can you hold chlorine for seven days without using tabs?
You can, but there are two reasons for not holding chlorine for a week: the physics side and the water quality side.
On the physics side, your pH ceiling is too high. As it climbs, you start to notice after 8.1 that chlorine is separating from CYA and getting zapped out by the sun. Alkalinity should never go below 50, and should stay between 60-65 in most pools in the summer. If we can handle that and limit the loss of chlorine, we can use chlorine much better.
On the water quality side, chlorine is bad at getting rid of oils. It makes them thick and sticky. If you get your pH ceiling down and use enzymes to remove oils, you’ll reduce chlorine demand, allowing you to hold it for seven days.
Q: What are the effects of high CYA on this whole process?
CYA transforms everything in your pool. A little CYA is a great thing. A lot is a really bad thing. This effect is not linear; it gets way worse the higher it gets.
You want to optimize chlorine protection while minimizing the downsides of slowing the chlorine down. Chlorine’s problem is that it can’t get to algae, and you use up a lot of chlorine trying to get it. CYA slows everything down to the point that you can’t keep up. The cheapest option is draining and diluting.
Q: How does high CYA affect alkalinity?
A: High CYA creates cyanurate alkalinity, which needs to be subtracted from total. Carbonate alkalinity will be in the 40s—this is no reason to freak out. 60-65 total is great, assuming you’re not adding too much acid to the pool.
Carbonate alkalinity will be less, because the higher your CYA, the more cyanurate alkalinity is in your buffering system, this has to be subtracted from your total, which lowers your pH ceiling. This is complicated math, but it’s all done for you in the app.
Q: Can you talk about the white rings around the aggregate again? Would this appear around tile inlays as well?
Yes, if it’s cement grout. There’s an Orenda article that covers this in detail.
Q: How do you reduce alkalinity?
A: With acid. And in Eric’s words, “Dilute, dilute, dilute, and crank up the turbulence.” Get the CO2 out so that the pH doesn’t tank.
Q: Can borates help reduce chlorine loss between services?
A: Yes, but not for the reasons you think. It’s good at suppressing the rise of pH, which keeps chlorine bound to CYA.
Q: Is your training available in Spanish?
A: Yes! Send an email to aiuta@orendatech.com or miguel@orendatech.com to learn more.
Q: Do you need to purge the pool with CV 600 for it to work properly?
A: Yes. With enzymes, you need an army of them. You can’t just use a weekly dose. You want to do a deep herbal cleanse, so start with a purge at the start of every season.
To learn more about LSI, visit Orenda Technologies’ website.
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