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How to Winterize a Commercial Swimming Pool

When summer ends, outdoor pools face an inevitable change in water chemistry. This change is driven by water temperature’s negative impact on water balance, as measured using the Langelier Saturation Index (LSI) or Ryznar Stability Index (RSI). This article covers how to winterize a commercial pool to prevent problems like etching, calcite crystallization, winter dust, and other problems. Read more

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Ways to Reduce Chlorine Demand

Chlorine demand is a common concern for commercial pools. Is your swimming pool consuming more chlorine than you would like, or more than it should be? There are many reasons why this can happen, so in this article we’ll explain a few of them, and offer a remedy for each.

What reduces chlorine?

Chlorine has two primary functions in water chemistry: sanitzation/disinfection, and oxidation.

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Reduction by Oxidation

The term “reduce”, or “reduction” of chlorine is the antonym to “oxidize”. The process of oxidation is the exact opposite of the process of reduction, which is why ORP (oxidation-reduction potential) is so commonly misunderstood.  Oxidation is the loss of electrons by an oxidant and given to an oxidizer. Reduction is the gain of electrons by the oxidizer (chlorine or perhaps ozone or a hydroxyl radical). Because electrons (e-) are negatively charged, they reduce the valence of the oxidizer.

Chlorine in its powerful killing and oxidizer form, Hypochlorous Acid (HOCl) is reduced by electrons into weak chlorides (Cl-) that can no longer oxidize (steal more electrons). Therefore, that chlorine has been reduced, or used up. It’s not free chlorine anymore.

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Metals are the first things to be oxidized when chlorine is added to water.

Compared to its strength as a sanitizer, chlorine is a relatively weak and inefficient oxidizer. Depending on what the oxidant is, its complexity determines how much chlorine will be consumed. Iron is easy to oxidize and occurs quickly. Sunscreen, on the other hand, is quite complex, and takes more chlorine to remove. And that’s nothing compared to a nitrogen compound like urea, which requires chlorine combining with ammonia and creating all sorts of disinfection byproducts (DBPs) like chloramines. These byproducts are measured as combined chlorine. See the breakpoint chlorination curve above.

Related: Water Chemistry Lesson: Combined Chlorine

Oxidation is chlorine’s method of eliminating non-living contaminants from water, like organic waste (bather waste, oils, sunscreen, cosmetics, lotions, etc.) and nitrogen compounds (ammonia, urea, etc.).

Reduction Consumption by Sanitization

Unlike oxidation, chlorine and other sanitizers do not steal electrons in the process of sanitization/disinfection, because the target contaminant is a living thing, not an oxidant. But like oxidation, chlorine also gets consumed in the killing process, it’s just not technically “reduced” because of electrons.

Sanitization is chlorine’s way of killing all living contaminants, and chlorine is really good at it. Killing germs and algae is what chlorine was made for. It is incredibly efficient at killing, whereas it is not so efficient at oxidizing complex non-living organics and nitrogen compounds.

Chlorine Demand

Let’s break down these demands into the two categories of sanitization and oxidation.

Sanitizer demand

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As long as chlorine’s kill rate is greater than the growth (reproduction rate) of the contaminant, the water will not be at risk of outbreak.

Living organisms that reproduce will consume chlorine. Naturally, these will be more prevalent in warmer water, because things like algae grow better in warm water. Cold water is not conducive to algae or bacterial growth…or at least, not nearly as fast. The name of the sanitization game is making sure chlorine’s killing speed is faster than the contaminant’s reproduction rate.

Algae are a huge part of chlorine demand in outdoor pools. Algae not only consume chlorine, they also consume carbon dioxide, which raises the pool’s pH, causing increased acid demand too.

Algae growth is almost always a consequence of overwhelmed chlorine, either by overstabilization, or by an abundance of nutrients like phosphates.

Germs and parasites are far more of a concern for the health and safety of a swimming pool, but fortunately, there are very few of them in the water, relatively speaking. Most germs and viruses are killed very quickly by chlorine (again, provided the pool is not over stabilized with too much CYA). Parasites like Cryptosporidium, however, are notoriously hard to kill, even with very high levels of chlorine. The contact time (CT) required to kill parasites is almost not even comparable to simple germs and other bacteria.  We could go on and on about recreational water illnesses (RWIs), but the CDC has already published the best RWI-prevention practices, and we are focusing on the consumption of chlorine for this article.

How to minimize sanitizer demand

To reduce the amount of chlorine consumed on germs, there are basically two ways you can attack the issue. First, and perhaps most obviously, is to optimize chlorine efficiency and strength.  One way is to supplement chlorine with a secondary disinfection system like UV, Ozone or AOP. This will take some of the burden off chlorine by killing just about anything that passes through the pump room. But therein lies the weakness of secondary systems: they are point-of-contact only. They do not offer a residual that can circulate throughout the pool itself–a fact that reinforces the need for a primary residual sanitizer like chlorine.

Not all secondary disinfection systems are ideal for any pool. UV, for instance, is not ideal for an outdoor pool because of a particular organic waste that is common in the water: sunscreen. Sunscreen blocks UV light, and therefore limits the efficacy of UV on outdoor pools. They still help, but they are not nearly as beneficial as something like Ozone or AOP.  Indoor pools, however, can benefit greatly from UV, though UV itself will gradually break down chlorine just like direct sunlight would.

Another option to supplement chlorine is with enzymes, though enzymes are not sanitizers. Enzymes handle the non-living organic oxidant demand–which happens to be the single-biggest category of contaminants in a pool–so there is more free chlorine available to kill germs. More on enzymes in a moment.

Optimizing chlorine isn’t just about strengthening it, it’s also about minimizing things that hold it back. Namely, cyanuric acid. CYA is beneficial for sunlight protection, but too much CYA dramatically weakens chlorine (%HOCl) and slows it down. Slow, weak chlorine means higher contact times (CT) when killing living pathogens.

phosphate removal, phosphate remover, concentrated phosphate remover, reduce phosphates, phosphate cloudThe second way to minimize sanitizer demand is to limit the growth and reproduction rate of algae. At any given time, an outdoor pool will be faced with algae spores trying to produce a colony. There is almost certainly more algae than there are germs, so we want to slow their growth and reproduction rates so chlorine can stay ahead. This can be accomplished by using Concentrated Phosphate Remover (CPR) as a proactive measure.

Oxidant Demand

Oxidants are the non-living contaminants in your water. The most common, by far, are non-living organics like sunscreen, cosmetics, lotions, deodorants, body oils, sweat, etc. Then there are the nitrogen compounds like nitrites, urea and ammonia, which eventually get reduced down into nitrates and other various disinfection byproducts. And depending on your tap water, metals can also be a major source of oxidant demand. Iron in particular can be a real nuisance.

How to minimize oxidant demand

Managing the oxidant demand dramatically reduces the overall chlorine demand.

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AAD enzyme purge

Depending on the oxidant type, there are several things that can help. Just like sanitizer demand, supplementing chlorine with secondary oxidation really helps. This does not include UV, because UV is not an oxidizer. We are talking about Ozone and AOP systems here. These systems help destroy non-living organics, nitrogen compounds, and pretty much anything else that can be oxidized. As mentioned earlier, we strongly recommend supplementing chlorine with enzymes like Amino Acid Digester (AAD). AAD breaks down and removes oils, sunscreen, cosmetics, mucous and most of the other things that come off our bodies. And because enzymes circulate alongside chlorine throughout the entire system, their benefit is 24/7 in every corner of the pool.

As for metals like iron, copper and manganese, they should ideally be pre-filtered out from the tap water fill line. If that’s not an option and metals are already in your pool, you can bet high iron levels will consume chlorine rapidly, and leave behind brown-tinted water or ugly stains. If the metals are in your pool, you can either sequester them or chelate them with Metal and Scale Inhibitor (MSI). But be aware, the first time you use MSI, its purge dose can wipe out your chlorine levels entirely for a few days (talk about a temporary chlorine demand!). That’s because it takes time for a chelating agent like MSI to find all the metals and minerals (like calcium) to bind to. Once it does its job, MSI coexists with chlorine just fine.


The vast majority of chlorine demand is from non-living organics, aka bather waste. The second biggest contributor is nitrogen compounds like urea and ammonia, which require a lot of chlorine to oxidize out of the pool. Then metals. Then there’s the sanitizer demand, which, unless you’re facing an algae outbreak, is proportionally much less prevalent in the water than the oxidant demand. Most of the sanitizer demand is small (but critically important for health and safety!), and chlorine is made for killing germs.

To reduce chlorine demand, consider supplementing chlorine with secondary oxidizers/disinfection systems, and enzymes. For metals in particular, MSI is a good option for chelation to prevent oxidation.

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Why remove phosphates?

Why remove phosphates? Just a few years ago, phosphates were a topic of debate in the swimming pool industry. Do they really matter? Are they fake news? Why is everyone talking about them, when they were never a problem ‘back in the day’?  Let’s get into it. Read more

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Calcium Phosphate Scale

Unless it has happened to you, it is tough to comprehend how severe of a problem calcium phosphate scale can be. Calcium phosphate is no ordinary scale (calcium carbonate); it is both physically harder, and harder to remove when it forms. On the Moh’s 1-10 scale of mineral hardness, normal calcium carbonate (calcite) is a 3, and calcium phosphate is a 5. In this artcile, we discuss what calcium phosphate is, how it forms, and the problems it can cause for swimming pools. Read more

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How to prevent metal stains and discoloration in swimming pools

Do you have metals in your tap water? Have you ever filled a pool and had the water get discolored when you added chlorine for the first time? If so, do you know why that happened? And more importantly, do you know how it can be prevented?

Dissolved metals are commonly found in tap water

dissolved metals, control metals, prevent stains, pool stains, MSI, next generation water science, remove iron, iron in pools, iron stainSource water is different everywhere you go, which is why we insist on testing tap water before filling a pool, or even servicing the pool. If you don’t know what is coming out of the tap, you will be at a severe disadvantage when it comes to managing pool chemistry. Since most pool operators test only a few factors–pH, total alkalinity, chlorine, and sometimes calcium hardness–otherwise predictable problems occur. To really grasp what will happen to the pool, one must know what is coming out of the tap.

If you have ever seen discolored water, or pools with metal stains, that’s an obvious sign of metal content in your water. Iron, when oxidized, turns brownish or orange in color. Stains will be ugly and visible to anyone looking. Copper has more of a light green, or even turquoise look to it when it gets oxidized. Manganese has a dark color, between black and purple, depending on the severity. It is also not uncommon to see a blend of multiple metals for unique colors and stains.

What causes metal stains and discoloration?

Metals are usually the first contaminants in water that chlorine oxidizes. This has to do with chemistry and the ease of oxidation. Here is a chart that shows the breakpoint chlorination curve, and it starts with the first thing chlorine attacks: metals.

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Metals like iron, manganese and copper are often the first things oxidized by chlorine.

The chart says in the first section “Destruction of chlorine residual by reducing compounds.” In this case, metals are the reducing compounds, because they get oxidized. Being oxidized means metals lose an electron and take on an oxygen from the oxidizer (chlorine, either HOCl or OCl-). After metals have been oxidized, at the expense of some of the free available chlorine, chlorine then begins to oxidize non-living organics and nitrogen compounds that form combined chlorine.

But let’s get back to metals. When metals are oxidized, they become a new substance altogether. It is usually with oxidation that metals become visible because of their color. Purely dissolved metals that have not been oxidized are normally invisible in water. In other words, oxidation of metals brings out their color in water.

Can metal stains be prevented?

control metals, pool stain, metal stains, iron staining, remove ironMetal stains in pools can be prevented. The way to prevent metal stains is to control metals. There are a few ways to control metals, but for the purposes of this article, let’s stay with what is practical in the pool business: removal, sequestration, and chelation.

How to remove metals from water

With certain types of filter media, metals can actually be filtered out. Such products do exist, but they can be costly. One such example is reverse osmosis, which takes just about everything out of the water…metals included. There are specific metal trapping filters that can be attached to hoses and plumbing that target heavy metals specifically as well. Some pool filters can also trap metals if they have a small enough filter media. Even so, with the help of certain sequestering agents, filters can capture metals to be backwashed or removed from the water.

If your metals are very high, removing them is a good idea. The less heavy metals you have in your water, the easier to manage.

Metal sequestration

Sequestering agents are common in the pool industry. Sequestering agents work kind of like a ‘metal magnet’, which attract metal ions into a cluster. When the electrons bind to the sequestering agent, oxidation of those metals can no longer occur, which is great! Sequestering prevents metal stains and discoloration of water. That being said, the metals are in suspension, and still in the water. The good news is, sequestered metals can more easily be caught by a filter and removed.

The challenge with sequestering metals is that most of the sequestering products are some kind of phosphate-based acid. Phosphonic acid is the most common type, and it is used even in municipal water treatment systems. Sequestering metals protects infrastructure and can also prevent scale in water treatment pipes. Normally this would be no big deal, except that phosphonic acid is basically liquid phosphates, and food for microorganisms like algae. So pool operators now have elevated phosphate levels to deal with.

What do you think happens when the pool operator uses a phosphate remover? The sequestering agent is wiped out, and the metals it was holding are now released back in the water, and available to be oxidized once again. The use of phosphate-based sequestering agents, therefore, should be used either temporarily for metal removal, or at least with the knowledge of their impact on phosphate levels.

Metal chelation

Chelation is similar to sequestration, in that it binds with metals and prevents oxidation (and metal stains). Unlike a sequest, which binds many metal ions together into a cluster of sorts, a chelant grabs individual metal ions. No clustering, just individual metal ions that have been chelated separately.

In our far-from-scientific lingo, we think of it like this: sequestering agents cluster metals and hold them in suspension; chelating agents grab individual metal ions separately and hold them in solution.

Our Metal and Scale Inhibitor (MSI) is an NSF-50 Certified chelating agent. It is not phosphate-based, and therefore compatible with phosphate removers. MSI is great at preventing stains and discoloration because it holds metals in solution and protects them from oxidation. That being said, MSI is not meant to be used to remove metals. When you hold metals in solution, they may pass through filters, unlike clustered metals bound to a sequestering agent.

Prevention is easier than Correction

“An ounce of prevention is worth a pound of cure.” – Benjamin Franklin

You can remove, sequester or chelate metals before they are oxidized. If you do, metal stains should not occur. Be sure to test tap water to know the metal content, so you know how much is being introduced on a weekly basis when the pool is replenished with water. Once stains begin to form, it may take citric acid to lift them off the surface, and that process is aggressive on plaster.

We hope this article helps you better understand metals, and gives you hope that yes, you can prevent metal stains and discolorations in your pool. If you have specific questions, contact us or your local NextGeneration Dealer.

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Combined Chlorine, Chloramines and Ammonia

Combined chlorine is a concern shared by commercial pool operators worldwide. But what is combined chlorine? How does combined chlorine form? Is combined chlorine the same as chloramines? If not, what’s the difference between combined chlorine and chloramines? The science is advanced, but as usual, we are here to distill the information down and simplify it for you.

What is combined chlorine?

Combined chlorine is chlorine that has combined with nitrogen compounds present in water. Such compounds include monochloramine, dichloramine and trichloramine (which actually off-gasses into the air). At least, the three types of chloramines are what most people are familiar with. Combined chlorine includes a myriad of other disinfection byproducts (DBPs) like chloroform and other trihalomethanes. There are too many to name in this article.

Combined chlorine is easy to measure. Simply measure the Total Available Chlorine (TAC) and subtract Free Available Chlorine (FAC) from it. TAC – FAC = Combined Chlorine (CC). It’s essentially a measurement of chlorine present that is no longer free and available. Once chlorine oxidizes and combines with nitrogen compounds, it is no longer free chlorine. That being said, combined chlorine still has some disinfecting power, albeit far weaker than Hypochlorous Acid (HOCl).

Some health departments have limits to combined chlorine levels. Some states set a maximum level at 0.4 ppm. If your pool exceeds that, the health department can get involved. We also know that most people can smell the “pool smell” of chloramines at any level above 0.2 ppm of combined chlorine.

Here is an example of calculating combined chlorine:

2.5 ppm TAC – 1.7 ppm FAC = 0.8 CC

The nitrogen question: how does it get into pools?

To understand combined chlorine, chloramines and other issues in pools, we need to start with a basic understanding of nitrogen. And how nitrogen gets into a pool. There are basically four (4) ways nitrogen can get in the water.

1. Naturally

Nitrogen gas itself (N2) makes up something like 80% of our breathable air. It’s very prevalent in our environment, but because Nitrogen gas has a triple covalent bond, living things cannot use it in its natural form. And yet, Nitrogen is needed by all living things, plants and animals alike. It is a micronutrient essential to life. So how is it used?

Certain plants (like legumes) and bacteria carry a special enzyme called nitrogenase that can break the triple covalent bond holding Nitrogen gas together. This allows for usable Nitrogen compounds to be formed, such as ammonia (NH3), ammonium (NH4+), nitrite (NO2) and nitrate (NO3). These compounds are found in soils throughout nature. Naturally, these forms of nitrogen can find their way into swimming pools, maybe through soil runoff, or dirt on our skin, etc.

2. Source water

Believe it or not, municipal water treatment plants sometimes deliberately add nitrogen compounds to water. They do this to produce chloramines, which have some disinfection power (but not much). The benefit of chloramines vs. chlorine, however, is staying power. Chloramines last a lot longer in the pipes than normal chlorine.

The downside of this is obvious: chloramines are introduced through the source water.

3. Bathers

One of the most common sources of Nitrogen, especially in commercial pools, comes from bathers. And I don’t just mean people, I mean any bathers. This includes ducks and other birds that enjoy your pool, dogs, and other living things. But for now, let’s focus on people.

There is a compound called urea that is found in human sweat and urine. Urea is primarily made up of ammonia (??), which is a nitrogen compound. Urea is the culprit behind campaigns against swimmers peeing in the pool, because urea takes a lot of chlorine to oxidize out of the water.

4. Pool and other cleaning chemicals

Finally, people add chemicals to (and around) their pools. Some chemicals are ammonia-based, such as deck cleaners, common algaecides and disinfection chemicals. We see this all the time. A pool operator has a mystery combined chlorine problem, but a low bather load. Come to find out, they clean their pool deck every night with an ammonia-based cleaner. Or they fight algae with an ammonium sulfate algaecide.  Be aware that these products work great in the short term, but leave nitrogen behind, which will become combined chlorine.

The combined chlorine process

In a nutshell, the combined chlorine cycle works something like this: nitrogen compounds in the water are oxidized by chlorine. It takes a lot of hypochlorous acid—the strong, killing form of chlorine—to convert nitrogen to its next form, and the next, and next, and eventually off-gassed out of the water.  We say “a lot of hypochlorous acid”, because eventually it takes a 15:1 molar ratio of HOCl to Ammonia to get it out of the water. 5:1 creates monochloramine. 5-10:1 converts monochloramine to dichloramine. And 15:1 creates trichloramine, which eventually off-gasses out of the water (and then becomes a nightmare for air quality).

The nitrogen cycle in a swimming pool gets really complex, with all sorts of chemistry reactions that can occur. What you need to know is chlorine will eventually oxidize nitrogen out, but not easily. Chlorine is a great sanitizer, but comparatively, it’s not so great of an oxidizer. Eventually chlorine will overpower nitrogen and get it out. This is known as reaching breakpoint chlorination. Breakpoint chlorination is when chlorine overcomes nitrogen and organic loading, and begins to build a free chlorine residual.

How to reduce combined chlorine and chloramines

Combined chlorine needs to be destroyed, either through secondary sanitation systems or enough chlorine to complete its oxidation. Chloramines will eventually go airborne as trichloramines, which then become an air problem. We strongly recommend both a proactive and reactive approach to addressing combined chlorine.

Proactive methods to reduce combined chlorine

Minimize chlorine’s burden on things like non-living organic bather waste so it can focus on germs and oxidizing nitrogen. Such an approach can be accomplished by use of NSF-Certified enzymes, like AAD. AAD (Amino Acid Digester) breaks down carbon-based organic waste in the water, which chlorine would otherwise have to oxidize. With AAD, chlorine has much less carbon waste to fight, and therefore it is freed up to go after nitrogen. AAD is highly effective at optimizing chlorine efficiency.

Another proactive approach is to manage water with a slightly lower pH, like 7.2 to 7.4. Why a lower pH? Because the lower the pH, the higher percentage % of HOCl your chlorine will be. This means your chlorine will be stronger.

To manage a pool with lower pH, however, pool operators must maintain water balance according to the LSI and/or Ryznar index. If you use our LSI Calculator App, you will see that a lower pH creates more aggressive water. To compensate for a lower pH, you will need to have an above-average level of calcium hardness or carbonate alkalinity. Calcium Hypochlorite chlorine is a great choice for pools looking to optimize chlorine efficiency with a lower pH.

Another proactive approach is to make sure cleaning agents used in and around the pool are free of ammonia and other nitrogen products. You might be surprised! A lot of pool deck cleaners are basically pure ammonia.

Reactive methods to reduce combined chlorine

Once chlorine has combined with nitrogen compounds, short of shocking the pool with a lot more chlorine (hyperchlorination), there are secondary systems that can help. Medium pressure Ultraviolet systems (UV) can be very effective at destroying monochloramine and dichloramine. Ozone is another secondary system which can both sanitize and oxidize. Both of these systems are proven to help.

Another technology, relatively recent to aquatics, can also help in a major way. It’s called hyper-dissolved oxygen (HDO). Without making sanitation claims, the principle of HDO is simply to dissolve a lot of oxygen into the water, which can accelerate oxidation throughout the body of water.  Unlike Ozone or UV, which are contained to the pump room—and therefore point-of-contact systems—HDO sends oxygen out into the pool, where it works alongside chlorine. Just like AAD enzymes, HDO can be out in the field where the people are, working to help chlorine get the job done.


To keep control over combined chlorine, do your best to minimize nitrogen introduction. Check chemicals for anything like “ammonium” in the label…and avoid using them. Optimize chlorine efficiency, either by lowering pH or using AAD enzymes (or both). Use a secondary system like UV, Ozone or Hyper-dissolved oxygen. These strategies can make a huge difference.

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How to remove and prevent scum lines

Scum lines are very common in pools

In our business (commercial swimming pools), almost every pool has a scum line. Yes, even gutter pools can have them. For the sake of this article, let’s define a scum line as a visible layer of deposits at the water level that adhere to surfaces: walls, ladders, rails, tile lines or gutters. These deposits are not always the same. In fact, we find they are usually a mixture of non-living organics and anything that adheres to them. Because non-living organics in pools are often sticky and/or slimy, any number of suspended contaminants can join in on the scum line party.

We have seen hair, lint, grease, dirt, leaves, and other fun stuff adhered to pool walls at the water level. We have also seen deposits of calcium carbonate scale, calcium phosphate scale, and dried salt.  This article will explain how and why scum lines form; and more importantly, how to prevent and remove existing scum lines.

Chlorine vs. Bather Waste

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Figure 1. 100 parts-per-million chlorine in a bowl of water, versus a small amount of WD-40. It congealed into a hardened mess. Is chlorine really cut out for oxidizing oils and non-living organics? Surely 100 ppm should be enough to handle a small amount of oil. Right?

Non-living organic waste, or bather waste, comes in many forms. Body oils, sweat, mucous, urine…but also what we put on our bodies: lotions, hair products, sunscreen, etc. All of these contaminants contribute to the oxidant demand that chlorine must overcome to do its primary job: sanitation. Have you ever seen what chlorine does to a high concentration of bather waste? We experimented with 100 ppm chlorine in a bowl of water with a squirt of WD-40 (a type of oil). See the Figure 1.

The reality is this: chlorine is designed to be a sanitizer. It has to overcome the oxidant demand in order to exceed breakpoint chlorination, but chlorine is inefficient at it. Rather than oxidizing the oil out of the water in the bowl, it actually turned into a sort of hard gel. Very odd, indeed.

This gel is very sticky and all types of dirt and debris can attach to it.  But why only at the water line?

Non-living organics and oils float

Who remembers the elementary school experiment where you pour vegetable oil into a glass of water? It floats and stratifies, because oil is less dense than water. This same principle applies to non-living organics. They act like greasy oils and float to the surface. This explains why scum lines are never found deep below the surface; they adhere at the water level only. Below is a video to demonstrate more on that.

The same ‘scum’ fouls filters and leads to costly sand changes.  That is, of course, unless you chemically refurbish your sand. Nobody denies that scum lines are a nuisance in a public pool. Lifeguards spend countless hours scrubbing them with brushes and tile cleaners, and sometimes have to use pumice stones to remove hardened scum lines. Okay, to be fair, the latter is when you have hardened calcium carbonate scale on the tile line…and we will address that in a moment. The point is, these scum lines never show up three feet underwater, or near the main drain, right?

They always show up at the water line because oils float. So let’s treat the oils accordingly.

Scale and scum lines are different, but can coexist

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Salt generators give off heat during electrolysis. They also release a byproduct of sodium hydroxide (caustic lye) which raises the pH and the saturation index of the water. High pH and heat tend to encourage calcium carbonate to fall out of solution and harden.

Because scale is often in the same location as a scum line, the two problems are associated with one another. The truth is, they are completely different problems caused by completely different factors. While scum is at the water line because non-living organics float, scale forms near the water line because of temperature. To be more precise, scale forms when the water is over-saturated with calcium carbonate (according to either the Langelier Saturation Index (LSI) or Ryznar Index). One of the factors in both of those indices is water temperature.

The warmer the water, the higher the LSI or Ryznar, and the more likely it is that calcium carbonate will fall out of solution and harden. That’s what we call scale.

Have you ever noticed that carbonate scale forms first in heat exchangers and/or salt cells? Or how about on your shower head or faucet at home? Hot tubs scale way more often than swimming pools. For visible scale in the swimming pool, calcium will always harden in the warmest areas first. Think of the sunniest, darkest tile that gets the hottest. Or a spillway. You can probably picture it in your head. If not, we have included some photos.

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Before and after treating the pool with MSI and balancing the water to LSI standards. The scale was gone in two weeks.

How to prevent and remove scum lines


AAD enzyme, pool enzyme, tile scum preventionThe first thing is to address bather waste with something other than chlorine. We recommend a commercial-grade enzyme like our Amino Acid Digester (AAD). It circulates throughout the entire pool along with chlorine to break down and digest oils and other bather waste. It bubbles off carbon dioxide and effectively removes the oily waste from the water. Following our dosing recommendations for your pool should prevent scum lines from forming.

If carbonate scale is involved, circulating Metal & Scale Inhibitor (MSI) can prevent scale from forming in the first place.


Already have existing scum lines? If they are just grease related, using AAD in circulation and raising your water level can help remove them without labor. That said, normally they form at or right above the water line, due to evaporation loss and the wet-dry effect. So you may still need to clean the tiles. No problem, just use a good tile cleaner. If there is carbonate scale, you may want an acid-based tile cleaner for quick removal. Just like AAD, however, MSI can gently remove scale on your water line…but does so gently over time. It also needs to be soaking the scale, so scale above the water line will need manual cleaning.

Thanks for your time, and if you have any questions or need help, contact us.

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MSI: One very dynamic pool chemical

Meaningful pool care in more ways than one

Think of the most dynamic pool chemical you know of. What does it do? When we think of the word “dynamic”, it suggests multiple uses and a range of positive results. Metal & Scale Inhibitor (MSI), to us, is one very dynamic pool chemical. It serves many functions, including the ability to both prevent and undo common problems in swimming pools and other water treatment systems. Let’s share some of them.

1. Preventative water chemistry

Water chemistry affects everything in a water system. If your water is corrosive, it can cause damage to surfaces and equipment. Conversely, if it is scale-forming, the scale itself can cause damage too; pipes with scale in them can increase water pressure and reduce flow rates.

The most important factor in preventing corrosion and scale is LSI balance. After that, it helps to have a chelant like MSI to hold minerals and metals in solution. Take calcium carbonate scale, for example. If calcium is held in solution by MSI, it takes a much more for scale to form. Think of MSI as allowing more grace to your water chemistry.

It’s not that MSI prevents these problems from happening…it’s that it gives you, as an operator, an advantage in handling minerals and metals.

2. Protecting pool plaster

Pool plaster is most vulnerable while it is curing. Plaster curing can take 30 days more more while the surface hydrates underwater and hardens. Given that calcium chloride is often used as an accelerant in plaster mix, it provides available calcium to water that is probably calcium-deficient. Water will stop at nothing to reach equilibrium. As the universal solvent, water dissolves whatever calcium it can find and bring it into solution for its own benefit; the most readily available source is plaster or tile grout.

But what about vinyl liner pools, or fiberglass? The LSI still applies, but the difference is water has no source of calcium. Therefore, low LSI water corrodes its way through everything trying to find it. The damage can be severe over time. For vinyl liners, this can mean fading, wrinkling or even wearing through the liner itself, allowing water underneath it. It’s no good.

MSI provides more grace to the LSI. In effect, it seems to buffer the LSI acceptable range, making it more difficult to form scale, and more difficult to corrode. Of course, this buffering benefit has its limits. At some point, the LSI can be so far out of range that no amount of MSI can stop the inevitable consequences. Use MSI immediately upon filling (and refilling) a swimming pool. It gives you more time to adjust the chemistry to get in proper LSI range.

3. Dechlorination

With any sequestering agent or chelant, one of two things happens: it gets oxidized by chlorine, or it wipes out chlorine. MSI’s initial “purge” dose wipes out chlorine. In most cases, this is an annoyance; chlorine must be hand-fed for two or three days to catch up, because otherwise the pool is unsafe. Fortunately, the weekly maintenance dose of MSI is small enough that it hardly has any impact on chlorine levels. More importantly, the good news about MSI is it will not be oxidized out of the water by chlorine. That means it stays in the water and works to your benefit over a longer period of time. It’s just the initial concentration of the purge dose of MSI that overpowers chlorine…and when dosed properly and evenly circulated throughout the pool, chlorine levels can maintain just fine.

Dechlorination is sometimes needed, however. For example, if you need to do certain types of maintenance, or bring chlorine levels down from recent hyperchlorination, MSI can help. Rather than using sodium thiosulfate, MSI can accomplish more than just lower chlorine. After all, you get the benefits of this dynamic pool chemical while lowering the chlorine level to where you want it.

Realistically, dechlorination is a rare need for swimming pools…but sometimes it’s urgent. MSI can drop chlorine levels down in just minutes.

4. Chelating Metals, Preventing Stains

metal oxidation, metal staining, stain removal, dynamic pool chemical

Metals are the first things to be oxidized when chlorine is added to water.

Metals are the first substances to be oxidized when chlorine enters the water. Oxidation can change the color of certain metals. Eventually, when the water is oversaturated with dissolved metals, or when they are oxidized, they can fall out of solution and stain. Just like with calcium saturation, water can only hold so much.

Stains come in many different colors, and there are entire businesses devoted to stain removal. We are not one of them…but again, MSI is a dynamic pool chemical.  Just like with calcium, MSI gives more grace to the water’s ability to hold metals in solution. With MSI in your water, metals have a far more difficult time coming out of solution and staining, because the metals are chelated.

Chelating metals means MSI isolates each metal ion and binds with them. Binding with metal ions prevents them from being oxidized.

rebar staining, pool stain, plaster stain

When stains originate from behind the plaster, the stains will continue to occur. MSI cannot prevent these types of stains.

Can MSI remove existing metal stains?

Over time, MSI has shown it can gently dissolve stained metals back into solution and lift them from the pool surface. We told you MSI is a dynamic pool chemical. Unlike acid-based products, however, this process is slow. You may want to combine its efforts with ascorbic acid (vitamin C) to speed up the process. That said, be sure that the stain in question is, in fact, caused by metals in the water. Some stains come from behind the pool surface itself, like rebar being too close to the surface. In those cases, MSI cannot prevent or permanently remove that problem.

5. Scale removal

Yes, just like removing stains, MSI can dissolve calcium back into solution as well. Of course, the long-term solution is LSI balanced water…but even then, hardened scale won’t move easily. MSI is the chemical to soften and remove scale deposits around your pool. It can even remove scale on spillways and water falls, as long as the MSI-treated water has time to affect the scale area. Raise your water level to remove scale on a tile line, for example.

dynamic pool chemical, MSI, SC-1000, orenda, scale remover, pool scale, waterfall scale

In a matter of weeks, MSI gently removed carbonate scale from this pool’s spillway. In addition, this pool used AAD enzymes. Look at the difference in water clarity!

Why use one dynamic pool chemical vs. multiple single-use chemicals?

Why not?

pool automation, becsys automated feed pump

Enzymes on an automated feed pump


Automated feed pump technology is simple, yet wonderfully dynamic. We at Next Generation Water Science encourage all of our commercial pool customers to feed their maintenance dose of our AAD Enzymes via an automated feed pump. Yes, you could pour in the weekly maintenance dose every week, but if you have automation, why?

Feed pumps never forget

Consistency is arguably the largest benefit of using automation in your pool system. We are human beings, and it’s not unusual for us to forget something now and again. With an automated feed pump, chemicals like chlorine and acid can be automatically fed into the system based on a signal from a sensor. For example, an ORP sensor knows what the pool’s conductivity is. If the ORP is dropping, the controller recognizes there is an increase in chlorine demand and adjusts the chlorine accordingly.

Operators cannot manually keep up with such real-time water chemistry. It would require constant testing and adjusting.

When it comes to our enzymes–Amino Acid Digester (AAD)–the product is a non-toxic, non-hazardous liquid that can be easily administered via automated feed pump. This allows for daily dosing of enzymes instead of manual pouring. It also gets the measurement exactly right, every time.

BECSys controllers and automated feed pump

becsys automatic feed pump, automated feed pump, pool chemistry controller, pool controller, chemical controller

BECSys controllers show pool operators great information about their water chemistry.

We love BECSys controllers for a few reasons. First and foremost, they are reliable and easy for operators to use. BECS displays show valuable metrics of pool chemistry to help an aquatics director make informed decisions about how to treat their water. For example, you can know, in real time, the pH, ORP and Temperature of the water.

It also shows you the LSI and Ryzner indexes, Calcium hardness (ppm), alkalinity (ppm), and a time stamp.

The BECSys controller and its subordinate automated feed pumps serve to regulate pool chemistry. It allows for 24/7 chemical balancing of any liquids: chlorine, acid, and yes, AAD Enzymes.

Automated Feed Pump vs. Manual Pouring

In commercial pools, there is no fair comparison between pool automation and manual chemical pouring. Automation removes human error in measuring and dosing frequency. It also reduces the risk of spilling chemicals and reduces operator labor. Furthermore, chemicals are more effective when added frequently at smaller doses versus large doses infrequently. For AAD enzymes, manual pouring is a weekly task. That task could be automated and broken into daily dosing of smaller amounts.

For enzymes, feed pumps need to be calibrated to a very low setting. Unlike chlorine and acid–which can be fed in large increments–enzymes are fed in ounces at a time. Contact your pool service company for help in calibrating the feed pump and chemical controller to pull this off.