The Langelier Saturation Index is a mathematical method developed by a civil engineer named Wilfred F. Langelier. The initial purpose of the LSI was to be used as a tool for coating water distribution pipes with a thin layer of protective calcium scale in order to prevent corrosion. A modified LSI process was developed sometime in the 1970’s for use in swimming pools primarily as a predictive method for determining whether the water is corrosive or scale forming. Calcium levels are important in the determination of a correct LSI. Calcium levels must be at a minimum of 150 ppm to determine correct LSI readings.

Natural soft water means it is surface water with little absorption of minerals, like calcium. Soft water is termed aggressive due to the fact that the water seeks to balance itself by taking minerals from cementitious surfaces and/or metal parts. In most cases there is little calcium found in naturally soft waters. This is different than water that is softened by a water softener. Water softeners work by exchanging the ions of calcium and magnesium with sodium ions. Unlike naturally soft water the softener does not present corrosion problems due to the presence of TDS from the sodium ions.

Hard water is deemed so due to the high presence of calcium and magnesium. In swimming pools high levels of total hardness consist of about 75% calcium. When calcium combines with the carbonate present in pool water it precipitates as calcium carbonate scale. High calcium also interferes with the effectiveness of certain chemicals, especially any cleaners. When calcium is combined with soap it creates scum which is waxy and hard to remove. In cooler temperatures calcium is more soluble in water, however when water temperatures increase calcium becomes more insoluble and will precipitate along with carbon as scale. This is a big problem for heat exchangers in hard water as scale will deposit and cause damage to the element. The damaging scale can be primarily in the form of either calcium carbonate or calcium phosphate.

High evaporation can cause a natural increase in hardness. The main way calcium is increased is through the addition of certain levels of calcium chloride or hardness increaser.  Calcium chloride is available in two concentrations either 100% or 77%. 0.9 pounds of 100% calcium chloride raises the calcium hardness level 10 ppm in 10,000 gallons of water. 1.2 pounds of 77% raises the calcium hardness 10 ppm in 10,000 gallons. Calcium chloride has an exothermic reaction in water and care should be taken when mixing and handling the bucket. It is advised to wear gloves when adding.

The primary way to lower calcium hardness is by draining and dilution. This is the most cost-effective process. There are reverse osmosis trailers that can come out to a facility and run pool water through the filters in the trailer to lower calcium without substantial draining. These are costly. The most efficient way is to conduct regular maintenance drains in order to lower and dilute out higher levels of calcium. There is a formula to determine how much water to drain based on the target level of calcium desired.

Let’s use 350 ppm as a target calcium hardness that we want to achieve in a pool with 600 ppm calcium hardness. The source water has a calcium hardness level of 150 ppm.

( PPM Condition of Pool Water) – (PPM Target) (PPM Condition of Pool Water) – (PPM of Source Water)

600 ppm

350 ppm

600 ppm

150 ppm

250 ppm

Divide by 450 ppm

In this case 250 divided by 450 would be 55% of the average depth of the pool. Average depth is determined by taking the shallow end and deep end in feet and adding the two numbers together and then dividing them by two. Example 3’ shallow end plus 6’ deep = 9/2 = 4.5 feet.  4.5 divided by 2 = 2.25’. Another way to do this is to take 4.5’ x 50% = 2.25 feet. In this case draining 2.25 feet  and refilling would take the pool water from 600 ppm to 350 ppm.

Like the human body too much or not enough calcium can lead to health problems. In a swimming pool the proper amount of calcium can function as the lifeblood of protection and good water quality.

Pool Hot Tub Alliance guidelines for calcium hardness are 150 ppm minimum and 1,000 ppm maximum. Recommended ideal level is from 200 ppm-400ppm. 350 ppm is a good target.

The clarity of water in public aquatic facilities is vital for the safety of patrons. The main reason is that when pool water becomes cloudy to a point of inability to see swimmers beneath the surface this becomes a drowning hazard. According to the Centers for Disease Control CDC 10 people die every day due to drowning. That is over 3,000 deaths a year. Ten percent of the deaths from drowning are related to cloudy or murky water as a contributing factor. Tragically, many cloudy water drownings occur even with supervision or lifeguards present.

Here is just one tragic example: On a hot Sunday in June 2011 Marie Joseph hopped into a Toyota Corolla with a group of friends to go and cool off at the Veterans Vietnam Memorial Pool at Lafayette Park in Fall River Massachusetts.  Two days after this Marie’s body was found floating in the public pool at Lafayette Park.  During the outing Joseph and a nine-year-old were playing on the slide. After sliding down together the nine-year-old surfaced and noticed that Marie had appeared to sink to the bottom and had not surfaced! The nine-year-old notified a lifeguard that Marie Joseph was underwater and in trouble.  The responses of the lifeguards at the facility are questionable but one of the undisputed results of the investigation afterwards showed that extremely cloudy pool water hid Marie Joseph from lifeguards, friends and police investigators.

Conclusions from the investigation stated that, “low visibility was the reason Marie Joseph’s body went unnoticed for two days after she drowned”. The Herald News July 1st, 2011.

A police investigation revealed that visibility in the pool was less than 4 feet below the surface.  Even though required by state law, the bottom of the pool was not visible at all!

There are numerous reports such as this that occur in public facilities and lead to drowning deaths. Even with lifeguards on duty cloudy water can hide drowning victims. In this case supervision of lifeguards is useless. The main point here is that cloudy water drownings are absolutely preventable when the victim can be clearly seen.

Water clarity is important because for public pools there is a standard for the clarity of the water. Public pools and aquatic facilities must meet the NSF recommendation of 0.5 Nephelometric Turbidity Units NTUs. This is the same recommendation as drinking water. In other words public pools need to be as clear as a glass of water. NTU’s are measured by a device known as a nephelometer which measures the turbidity of the water in digital read outs. Health inspectors who don’t carry a device with them will use a visual means of evaluating clarity by standing at the deck and looking to the deepest part of the pool where the main drain is usually located. The inability to see the main drain clearly is the cause for immediate closure of the pool.

There are many causes of cloudy water. Everything from a lack of sufficient sanitizer to incorrect water balance. In particular high Total Dissolved Solids TDS and high Calcium Hardness are two main culprits of water balance that can cause cloudy water. TDS levels should be managed so as not to exceed 1,500 ppm over the start up water.  Excessive bather load and an influx of contaminant waste will cause pool water to become cloudy very quickly.

When cloudy water begins to become an issue the first thing to check is the filtration and circulation system. If it is a sand filter system check to ensure that there is a proper amount of sand in the filter tank. Also, check for mudballs in the sand media that could burrow through the sand bed and cause channeling. These are tunnels through the sand bed that will lead to unfiltered water going back to the pool.  Also, if the sand is new it may not filter as well. In the case of brand-new sand or media it is recommended to use a clarifier in order to make small particulate matter more filterable. Cartridge filters may need cleaning or replacement and Diatomaceous Earth D.E. the media may need to be backwashed and replaced. Also, the grids should be checked for holes which would allow D.E. to pass through into the pool, causing haziness from the media in suspension of the water. Other things to check are the pump pots and skimmers for any accumulation of debris. Check the flow of the system to ensure there is not a clog somewhere. Also, check for suction leaks that allow air into the system.

While water clarity is important for safety it can also have an impact on the efficiency of Ultra-Violet UV systems as well. UV works by high energy low intensity light waves that disrupt the DNA of microbes. Water with excessive amounts of particulate matter present will cause the light rays to deflect so they can not hit the microbes. An excess of body oils and particles can also lead to clogging of filters and interference with probes.

In the case of pool water clarity it is better to be proactive than reactive. If the pool is already cloudy then it will need to be closed until the water is cleared. Proactively managing water clarity means first having the proper filtration and circulation system to ensure that the entire amount of water in the pool is passing through in 6 hours. This is the standard turnover rate code. Also, ensuring that the filter is sized properly to the flow of the pump. So, proper turnover, proper flow rate and proper filter size. Taking a CPO course can walk you through how to determine all of these correct circulation and filter rates.

Chemical solutions include the use of a natural based chitosan clarifier, especially for sand filters. Enzymes can break down oils that can combine with dirt and foul up filters and probes. Additional oxidation such as ozone, UV or shocking with liquid chlorine help to keep combined chlorine levels managed and oxidize non-living particulates. Clear water is really the number one priority when it comes to a public aquatic facility. Proactively managing water clarity will bring increased safety to the patrons and additional peace of mind for the operator.

Health inspectors concern themselves with two aspects of pool water. One is the disinfection, and the other is the pH.  As far as water balance is concerned the main value from a human health concern is the pH. That is because the pH is a determiner of proper disinfection based on its role in the production of the killing agent of chlorine which is HOCl. A high pH exceeding 8 will dangerously inhibit proper disinfection from chlorine.  An extremely low pH below 7.2 will lead to rapid consumption of chlorine. So, from a health stand-point pH is vital. When it comes to overall control of water balance and protection of surfaces and pool equipment total alkalinity plays a more vital role because it will always determine where the pH is going. Total alkalinity is the buffer for pH. Primarily, total alkalinity acts as a buffer to keep the pH from going down. It acts as an anchor to keep the pH from drifting down or up. While it primarily works to reduce pH decrease it can hold the pH in a more stable range based on what chemicals are added to the pool water.

Total alkalinity consists of three constituents as follows:

• Bi-carbonate HCO_{3 –}
• Carbonate CO_{3 -}
• Hydroxide OH-

The bi-carbonate form of alkalinity is the most predominant in pool water with a pH between 7.2 to 7.8.  When alkalinity is high in the carbonate form it tends to drive the pH low. This will lead to a lack in buffering causing the pH to bounce lower and higher depending on the type of chemical added. With high hydroxide the pH increases due to the lack of carbon dioxide CO_2.  pH increases as carbon dioxide leaves the water. A high total alkalinity will lead to what is known as pH lock. This is a result where the pH becomes difficult to move up or down.

Additional problems from a too low alkalinity include:

• Etching of the pool surface
• Staining
• Corrosive water

When the alkalinity is too high additional symptoms are:

• Cloudy Water
• Rough surfaces from scaling
• Clogged filters
• Poor circulation
• Scaled heater exchangers.

There are other interferences to total alkalinity from pool water. This includes cyanuric acid CYA, borates, and phosphates.  Of all of these CYA plays a more prominent role in contributing to the total alkalinity test.  At levels of 60 ppm or above of CYA there may be a one third interference on the high side for total alkalinity. When the CYA in the pool is at a level of 60 or above then an adjustment must be made to obtain a true alkalinity reading. Below is an example:

Total alkalinity test reading 100 ppm.

CYA test reading of 60 ppm ÷ 3 = 20 ppm

20 ppm subtracted from 100 ppm = 80 ppm true alkalinity

Keep in mind that the standard recommendation from the Pool Hot Tub Alliance (PHTA) for CYA is between 30 to 50 ppm. At these levels there should not be a significant interference in the total alkalinity test.

To lower total alkalinity either liquid muriatic acid or dry sodium bisulfate can be added. With liquid muriatic acid 31.4% it takes 25.6 fl. Oz to lower the total alkalinity by 10 ppm in 10,000 gallons of pool water. To lower the total alkalinity using sodium bisulfate it would take 2.1 lbs. for a 10 ppm decrease in 10,000 gallons of water. One of the biggest challenges that commercial operators face is in keeping both the pH and total alkalinity values balanced in order to ensure sufficient disinfection and protection of the pool surfaces and equipment. The biggest challenge is that both acid and basic chemicals affect the pH and total alkalinity. When acid is added it will lower both the total alkalinity and the pH.  If sodium carbonate (soda ash) is added it will increase the pH and the total alkalinity.  Sodium bi-carbonate (Bi-carb baking soda) will work better than soda ash at increasing total alkalinity however it can still have an effect to raise pH at least to 8. There can be a definite struggle in trying to lower the pH without also lowering total alkalinity and conversely raising a low pH without causing an increase in total alkalinity is challenging.

One of the best ways to adjust a high total alkalinity and pH is to focus on the lowering of the alkalinity into the ideal range between 80 to 120ppm by using muriatic acid at 25.6 oz. per 10 ppm decrease in 10,000 gallons. When doing this it will no doubt lower pH beyond the 7.2 limit. The best thing to do in this scenario once alkalinity is lowered is to raise pH to 7.4 – 7.6 range by using aeration. This can be done by turning on waterfalls or fountains or adding an aerator to the return or using a submersible pump placed on a step with a pvc elbow pointed up and out over the pool water. Any method of creating aeration and turbulence in the water will cause the pH to increase without having an effect on the total alkalinity. So, the total alkalinity can be set at ideal ranges and pH can be targeted in ideal as well with using air.

This would rarely happen because when using aeration the closer the pH gets to reaching its ceiling the rise of the pH will slow down considerably. In other words, typically the ceiling of pH that exists when CO2 is being driven out of the water is a little over 8. This is considered the equilibrium constant. So the closer the pH gets to reaching equilibrium the slower it goes.  A pH of 7.2 will increase faster from aeration than a pH of 7.4. It will take an exceptionally long time for the pH to rise from 7.6 to 8. If the process is monitored there really is no way the pH can spike from using aeration and since this article is about total alkalinity this is the best way to balance between the two.

In conclusion it is vital to understand that total alkalinity determines where the pH will go. A high total alkalinity will lead to pH increasing and a low total alkalinity will cause pH to drift downward. If high pH is a consistent problem then it may be best to run the total alkalinity at the lower ideal range of 80 ppm. In cases where cal-hypo or sodium hypochlorite sanitizer is used adjusting the total alkalinity towards the minimum of 60 ppm will help to hold the pH down as well. In cases where pH tends to drop or if an acidic form of sanitizer such as tri-chlor is used then the total alkalinity should be managed closer to the high ideal of 120 ppm.  The understanding of total alkalinity is what will help to ensure a proper pH and very stable water quality.

One of the best algae preventers and algaecide is chlorine. More specifically free chlorine FC and even more specifically hypochlorous acid HOCl. It takes just 0.05 ppm of HOCl to effectively prevent and inactivate algae in a swimming pool. In a swimming pool FC consists of both HOCl and hypochlorite ion OCl-.  HOCl is a 99% killing agent while the OCl is only 1%.  In order to ensure the greatest prevention and killing of algae in pool water we must have sufficient HOCl.  pH and temperature of the water play an important role in the production of HOCl. In a pool with a pH of 7.5 and temp of 86 degrees F 30 degrees C there is 50% HOCl and 50% -OCl. This is in water with no cyanuric acid CYA present, so in this case there would be more than enough HOCl to keep algae out at FC levels of 1ppm-4ppm. If the pH were to rise to 8.0 in this 86F 30C pool the HOCl would go down to 24%. In this case the FC levels would need to be 3-4ppm in order to keep algae out. Again this is water with no CYA present. This plainly shows that there is more algae fighting power from chlorine at a lower pH.

Now if we add CYA at a level of 30 ppm things change considerably and maintaining a FC level of 1ppm-4ppm may not be sufficient to keep algae from blooming in the pool. Here’s why; In a pool with 30 ppm of CYA and a pH of 7.5 there will still be 50% HOCl and 50% OCl- as FC. However now with 30 ppm of CYA 97% of FC is bound to the CYA and only 3% FC is available to disinfect and deal with algae. So, in this case if we take 3% and divide by two we have 1.5% active HOCl and 1.5% active OCl-. The following example shows the effect that CYA has on chlorine’s ability to prevent algae at FC levels of 1ppm-4.0 ppm. We need at least 0.05 ppm of HOCl in order to prevent algae.

1. ppm x 1.5% =0.015 ppm HOCl Not enough to kill algae
2. ppm x 1.5% = 0.03 ppm HOCl Not enough to kill algae
3. ppm x 1.5% = 0.045 ppm HOCl Still not enough to kill algae
4. ppm x 1.5% = 0.06 ppm HOCl Finally algae is killed

As CYA levels increase more chlorine will be needed in order to create the sufficient level of HOCl needed to keep algae from growing. pH is still important in this scenario and maintaining a lower pH will help to provide a higher percent of HOCl. With a pH of 8.0 and CYA of 30 ppm there will be a 15% reduction of HOCl in the pool.  This means the pool would have to be maintained no less than 4 ppm FC in order to keep algae out of the pool. In contrast if the pH were lowered to 7.3 there would be more than sufficient HOCl at just 2.0 ppm to kill and prevent algae. Managing both pH and CYA is a giant step towards keeping algae from blooming in the pool.

Algae is a plant and like most plants it needs nutrients in order to bloom. The two main nutrients it needs are nitrates and phosphates. Nitrogen is introduced from lightening and rainstorms as well as from swimmer waste and well water. At proper levels of FC nitrogen in the form of nitrites will be oxidized out of the water. If FC level is too low then nitrites will convert to nitrates which can not be oxidized and will accumulate as food for algae. Algae can become a problem at nitrate levels of 10 ppm. Nitrates can only be removed by draining some of the water out to lower the ppm level.  Another prime nutrient for algae growth is phosphate in the form of ortho-phosphate. Phosphates are contributed into pool water from many sources. The two main contributors of phosphate into pool water are from metal sequestering products used to prevent scale and staining and source fill water. Many metal and scale prevention products contain phosphonic and phosphoric acid. While these are not direct nutrients after reaction to metals and hydrolysis the by product will become ortho-phosphate which is a direct nutrient. The biggest culprit of direct phosphate nutrient comes from source water. A majority of water treatment facilities in North America are mandated by the Environmental Protection Agency EPA to practice corrosion control of underground pipes in order to prevent the leaching of lead or pathogenic micro-organisms into the supply chain. One of the most widely used corrosion control systems is to use an anti-corrosion chemical. Straight orthophosphate is added to drinking water systems as an anti-corrosion method for lead and copper and is recommended by the EPA. One way to determine the presence of orthophosphate in fill water is to do a orthophosphate test of the source. Most test kits and strips in the pool industry are designed to test for orthophosphate which is a direct nutrient for algae growth. To take this a step further orthophosphate is classified as a “growth limiting nutrient” for algae according to lake and pond science. This means that the presence of orthophosphate in water is crucial to the healthy growth of algae. When you remove orthophosphate from the water even if there is still nitrates present; the growth of the algae is seriously limited. Nitrates can only be removed by draining water from the pool and obviously this will reduce phosphate as well. However, phosphate can be placed back into the pool just as a result of re-filling. So, it is recommended to test source water and pool water, then treat the pool water with a phosphate remover. Zero phosphate would be ideal, however, in today’s world that would be very difficult. Best is to work at keeping the phosphate level below 200 part per billion PPB. Managing nitrates and phosphates and keeping levels down will go a long way in not only preventing algae, but also in chlorine savings. One of the biggest consumers of free chlorine is when there is algae present that is feeding on nutrients.

A very proven and effective way to prevent algae is to add borates to the pool. At a level of 50 ppm borate will do two things that reduce the ability of algae to grow. It should be understood the borate won’t kill existing algae that has already bloomed. Borate is considered an algaestat rather than an algaecide. While it cannot effect bloomed algae it acts as an inhibitor preventing cell wall development, metabolism and cell division. If left unchecked algae cells have the ability to divide and double in population within 3 to 8 hours. If the algae is allowed to reach this stage it will consume chlorine and visible algae will appear. Since borate prevents the cell division process algae can’t grow and cannot consume chlorine that is present in the pool water. Borate also acts as a buffer to prevent the pH from increasing. We already determined that chlorine is more effective to kill algae at a lower pH so if the pH is controlled from increasing then it will be harder for algae to grow. Also, because borate acts as a softener of the water then chlorine and algaecides will penetrate any algae spores more readily.

The best and most cost effective type of borate product is boric acid. It takes 47.5 lbs of boric acid to get 50 ppm in a 20,000 gallon pool.

These are some best water quality practices that will help to reduce the potential for algae to get a foot hold in pools.

• pH 7.2 to 7.5-the lower the better
• CYA no more than 30 ppm
• Phosphates below 200 ppb
• Nitrates less than 10 ppm
• Borates at level of 50 ppm

Algaecides can be used and are recommended during warm weather and heavy swimming season. Poly-quat is one of the best all around algae preventors and especially good in the prevention of green free floating algae. Copper based algaecides are especially good against blue green forms of cyanobacteria, black algae and yellow algae. As long as pH remains balanced staining from metallic algaecide will not be a problem. There are also green swamp to clear products which incorporate the use of sodium ammonium combined with chlorine to bring the pool from green back to blue within 24 hours. These are all additional tools in the fight to keep algae out of pools. Good water quality practices and regular brushing of pools are still the best foundational routines for prevention.