The Most Important Chemical In Your Pool Water
Updated: May 29, 2019
Total Alkalinity is the most important factor in maintaining balanced swimming pool water because it governs pH which in turn affects Chlorine.
If you want to ensure balanced #pool water, reduce the potential of fluctuating chemical levels, and minimize the amount of #Chlorine and #Acid you've been adding to your pool, you should make Total Alkalinity a top priority. It's the number one factor in maintaining a stable #pH level which directly affects your Chlorines ability to work as a #sanitizer.
Carbonates, Bicarbonates, & Hydroxides
Pool #water #chemistry isn't rocket science but understanding how to properly balance and maintain crystal clear water can become fairly involved. And if you don't have a complete understanding of at least how your pool chemicals work together to achieve happily balanced water, you'll probably struggle to keep your water chemistry in check.
In my experience, most people are actually unfamiliar with all 5 chemicals required to achieve perfectly balanced water and tend to overlook what I believe to be the most important of these chemicals. Of the 5 pool chemicals required to maintain balanced water in a standard pool, 3 of them are essential: #Chlorine, #pH, and #TotalAlkalinity. But, during my years as a service tech., I've found that Chlorine and Acid, generally receive the most attention while Total Alkalinity, which is the third and most crucial chemical, takes a back seat.
Pools typically require a consistent dose of Chlorine and Acid because Chlorine gets depleted as it attaches itself to bacteria in order to kill it or it gets extracted by the sun (depending on your Stabilizer levels) and Acid compensates for the increase in pH caused by the addition of the Chlorine. The other solid chemicals like #SodiumBicarb, which is commonly used to increase a pools T.A., along with #Calcium, and #Stabilizer, once added to the pool, remain in the water as dissolved solids. The only way to lower these chemical levels is by diluting them through the addition or subtraction of water via rain, a fresh water source like a hose, splash out or evaporation.
And unlike Chlorine and Acid, these chemicals, depending on the pool, can sometimes go months or even a full year without needing another dose. So it's not uncommon for service techs and homeowners not to give them as much attention as they should. Especially considering you can still maintain relatively clean water even when your #Alkalinity, #Calcium, or #Stabilizer is unbalanced - but it's also much more difficult. So instead of taking the time to properly test and balance all 5 chemicals on a regular basis, I find most people tend to just add Chlorine and Acid more often than necessary because it's much more convenient, still keeps the pool water blue for a time, and they aren't the wiser to the effects of the water chemistry until it's too late and they start to experience algae or cloudiness.
But in places like Miami, where pools get heavy use and rain, these dissolved solids can also become saturated fairly quickly and even more so if your pool or equipment leaks and you're constantly adding water - which by the way is The Worst Thing You Can Do To Your Pools Water Chemistry. So in some instances, they need replenishing more often than you'd think which is why most people experiencing difficulties with their water chemistry, frequently have unbalanced Alkalinity, Stabilizer or Calcium levels.
And what most people probably don't realize is that the Chlorine they're relying on to keep their water free of bacterium, can be affected by the 4 other chemicals in the water, especially the pH. In fact, Chlorine is directly affected by the waters pH level and pH is regulated by Total Alkalinity. So while #Chlorine and #pH are two essential factors in maintaining proper water balance, they are both actually dependent on #TotalAlkalinity. In my opinion, this makes T.A. the most important chemical in your pool water.
Why you should trust me
I'm a second general pool professional so I've been running around cleaning pools, testing pool water and adding chemicals since I was in diapers. I even got liquid chlorine directly into my eye when I was only eight years old - I'm OK now. I've serviced Residential and Commercial properties ranging from 800 gal. spas to 200,000 gal. aquatic facilities like Barry Universities Pentafort pool, Brickell Place's Condominium pool, Double Trees Ocean Point Condominium pool, and both the Heritage Park and Government Center Fountains for the City of Sunny Isles.
I've also acquired an Associates of Science degree in Aquatic Engineering from Keiser University completing the relevant coursework for Basic Chemistry, Advanced Water Chemistry, Cleaning Technology, and Filtration Technology. I've read Taylor Technologies Pool & Spa Water Chemistry Booklet, front to back on more than one occasion and spoken to plenty of industry professionals in the field and at conferences regarding water chemistry issues and solutions. I also pay attention and read up on industry related topics and current events relating to water chemistry like when the Olympic pool in Rio turned green in 2016.
Why Total Alkalinity
Total Alkalinity is a prime ingredient in maintaining balanced swimming pool water and it's actually one of the primary elements measured in water chemistry in general. It's one of the best measures of the sensitivity of the water-to-acid inputs and without it, any acids added to a stream or pool, for instance, would cause an immediate change in the pH which could have harmful affects. Even government organizations like the EPA take TA samples from bodies of water in order to determine its ability to neutralize acidic pollution from rainfall or wastewater. Alkalinity control is also important in many other processes including municipal water and wastewater treatment, paper and textile manufacturing, commercial laundering, warewashing, beverage production, and boiler and cooling system operations.
The same principle applies to your swimming pool water. The waters TA level is the measure of the ability of the water to resist changes in pH upon the addition of acids, bases, or other pH altering agents. In other words, it's the ability to buffer water from wide and rapic pH fluctuations. And pH control is critical because in water that contains no buffering ability, pH can wander dramatically between acidic and basic levels resulting in highly unbalanced water, bather discomfort and affects sanitizer efficiency.
Low pH can cause damage to pool liners, permanent damage to the surface like etching, scaling, and pitting, corrode metal components like light rings, ladders and copper heat exchangers, and even cause bather discomfort by irritating your skin and eyes. It will also reduce the level of your TA, further compounding the issue. On the other hand, a high pH can cause scale formations, leave metal stains, cause cloudy water and bather discomfort as well as reduce the overall effectiveness of your Chlorine which creates an entirely separate set of problems.
To give you an idea, pH is measured on what's referred to as the pH scale, measured from 0 – 14, with a pH of 7 being neutral. Below 7, the water is acidic and above 7, the water is alkaline or “basic.” In other words, the stronger the acid, the lower the pH number, and the stronger the alkali, the higher the pH number.
It's also a logarithmic scale, meaning that every whole unit increase is 10 times its predecessor. So, the difference between each whole number, say 6 and 7, is a factor of 10. That means from 7 to 8, the water is 10 times more alkaline and from 7 to 9, it's 100 times more alkaline. Therefore, a pH of 6 is 10 times more acidic than a pH of 7 and a pH of 3 is 10,000 times more acidic than a pH of 7. So even small changes in pH can have large effects.
In this case any variation between the waters pH level not only affects the pool, its components and bathers, but it can also have a significant impact on the Chlorines ability to work as a sanitizer. Chlorine or Sodium Hypochlorite is actually pH dependent meaning the pH determines how effective the Chlorine will be in the water. The lower the pH, the stronger the Chlorines killing power but the higher the pH, the less effective Chlorine becomes. According to the National Swimming Pool Foundation's Pool and Spa Handbook these are the effective percentages of Chlorine or Hypochlorous acid relative to the level of the pH:
HOCl: 97% - pH: 6.0
HOCl: 91% - pH: 6.5
HOCl: 76% - pH: 7.0
HOCl: 66% - pH: 7.2
HOCl: 50% - pH: 7.5
HOCl: 33% - pH: 7.8
HOCl: 24% - pH: 8.0
HOCl: 9% - pH: 8.5
So with a pH level of 6.0 your Chlorine is the most effective with 97% oxidation available to kill bacteria and algae. Keep in mind this is just an example and a pH of 6.0 would result in extremely acidic water that's unsafe to swim in. On the flip side, if your pH is at 8.5, only 9% of your Chlorine is available to work as a sanitizer. And in the field, I've found that most people tend to have a pH level that's too high rather than too low. And even if your pH is only slightly on the high side, between 7.8 - 8.0, your're still basically cutting your Chlorines effectiveness in half.
Having less effective Chlorine in the water will take the sanitizer longer to do it's job and give harmful bacteria more time to grow. This also usually leads to people wondering why they have a good Chlorine reading but cloudy water. It's also why simply adding Chlorine to the water won't necessarily solve your problems. Especially if your dissolved solid chemicals are also out of wack.
But if you keep your pH in the ideal range, your Chlorine is usually around 50% effective which is usually more than enough to adequately sanitize the water. A Chlorine level between 2 - 4 ppm, will effectively kill most pathogens almost immediately. The easiest way to regulate a stable pH level to ensure effective Chlorine, is by having a balanced TA level.
It's also important to understand that the type of Chlorine you use affects both your pH and Alkalinity levels because different types of Chlorine have different pH levels. For example, Trichlor has a low pH of about 3 but Calcium Hypochlorite has a pH of almost 12. So depending on the type of sanitizing chemical you add to your water, it will either raise or lower your pH. And if you don't have a balanced TA level, this can have a dramatic affect on the pH which could potentially render the sanitizing agent you just added to the water, "useless."
So understanding the relationship between all 3 essential chemicals that are Chlorine, pH, and Total Alkalinity, can dramatically affect the outcome of your pool water chemistry. And you should start with your Total Alkalinity because unbalanced TA results in unbalanced pH which in turn, results in inefficient and ineffective sanitization. This creates a compounded set of problems for the pool. So without a proper Total Alkalinity level you will never truly achieve balanced water and you'll find yourself constantly battling your water chemistry by adding excess amounts of Chlorine and Acid, arguably doing more harm than good.
pH stands for "potens hydrogen," which is Latin for “hydrogen power,” as acidity is caused by a predominance of the chemical species H+ or the hydrogen ion. So really your pH is just the concentration of hydrogen ions in any given substance. This means acidic solutions have more hydrogen ions than alkaline or neutral solutions.
When you immerse acids and alkalis in solution, they release free ions. In a water-based solution, an acid releases positive hydrogen (H+) ions while an alkali releases negative hydroxide (OH-) ones. This means when an acid is dissolved in water, the balance between hydrogen ions and hydroxide ions changes, resulting in more hydrogen ions than hydroxide ions in the solution - an acidic solution.
The balance also changes when an alkali is dissolved in water, but in the the opposite way. In this case, the solution ends up with more hydroxide ions than hydrogen ions - an alkaline solution. When a solution is considered neutral – the concentration of hydrogen ions is equal to the concentration of hydroxide ions.
Acids react very strongly to metals and when concentrated, can be very corrosive.
Alkaline solutions on the other hand, have fewer hydrogen ions than neutral or acidic solutions or acids. But like acids, strong alkalis can also burn your skin.
In swimming pool water, you want your pH to be between 7.4 - 7.6. which is slightly alkaline but it's more comfortable for the bather because the pH of the human eye is 7.5. So if you've ever opened your eyes underwater before and they burned, it's usually because the pH is off, which instead is commonly mistaken as having too much Chlorine in the water. Human blood also has a slightly higher-than-neutral pH of about 7.4.
It's also worth sharing that pH was invented to measure the acidity of water in the brewing of beer in the early 1900s :).
Testing your TA
Unlike pH, which is basically an equilibrium scale to measure against, Total Alkalinity is a measurement of the concentration of all alkaline substances dissolved in the water. These substances are primarily #carbonates, #bicarbonates and #hydroxides, along with a few others like borates, phosphates, and silicates. So Total Alkalinity is not measured on the pH scale, it's measured by its concentration in parts-per-million (ppm), rather than how alkaline the water is. Typically the ideal range is between 80-120 ppm but depending on the type of sanitizer used, the APSP has suggested ranges.
According to the APSP, ANSI/APSP-11, the American National Standard for Water Quality in Public Pools and Spas states that Total Alkalinity shall be maintained between a minimum 60 and a maximum of 180 ppm as Calcium Carbonate or CaCO3 . But because some pools use different types of sanitizers with different chemical makeups, the recommended range can vary. Either way, as a rule of thumb, you can't really go wrong with a TA level between 80-120 ppm.
However, ideally, Total Alkalinity should be maintained between 80 and 100 ppm as CaCO3 where chlorine generators, calcium hypochlorite, lithium hypochlorite, and sodium hypochlorite are used, because these sanitizers cause the pH to rise.
The ideal range where sodium dichlor, trichlor, chlorine gas and bromine compounds are used is between 100 and 120 ppm as CaCO3, because these sanitizers will cause the pH to drift downwards. Certain systems such as PHMB are relatively unaffected and don't impact TA.
For example, Trichlor has a low pH of about 3, which means you will want your total alkalinity closer to 120ppm, given how acidic Trichlor is. Liquid Chlorine or "bleach", however, has a high pH of about 13, so you want a lower alkalinity, closer to 80-100ppm because one of the byproducts of using liquid bleach or Sodium Hypochlorite is Sodium Hydroxide, which contributes to Total Alkalinity and raises pH.
There are also two types of alkalinity tests, #titration and #colorimetric. The more accurate test is titration. However, high chlorine and bromine levels can cause the endpoint color of the titration to be yellow, or colorless, instead of pink. So if you've ever tested your water using reagents and kept getting colorless readings, it might be because you're sanitizer levels are too high and they're "bleaching" the colors out. The addition of a chlorine inhibitor, such as sodium thiosulfate, before a titration test will neutralize the chlorine or bromine and give the correct endpoint color. Many algaecides also contain quats (quaternary ammonium cations) or polyquats. High levels of these can cause low readings in colorimetric alkalinity tests. Inhibitors are added to minimize this interference but over dosing with these algaecides can cause errors in alkalinity readings. Very high levels of biguanide have also been known to cause a similar reaction.
Alkalinity which mainly includes carbonate, bicarbonate, and cyanuric acid, is determined by titration with a standard acid to a desginated pH and recorded as TA. In other words, it's physically measured by measuring the amount of acid (e.g., sulfuric acid) needed to bring a water sample to a designated pH and recorded as either P, M, or T alkalinity. Total Alkalinity is titrated to an endpoint pH of 4.5 using a blended indicator (bromocresol green/methyl red). By measuring the volume of acid added during the titration, the amount of base present can be calculated. At this pH all the alkaline compounds in the sample are "used up." The result is reported as milligrams per liter of calcium carbonate (mg/L CaCO3). If sulfuric acid is being added to modify pH, it will also alter the alkalinity relationship.
For the most accurate readings, you should be using The Best Swimming Pool Water Chemistry Test Kit. Taylor technologies recommends your Chlorine and pH be tested daily and your T.A. weekly. And although I don't necessarily think it's crucial to test these chemicals daily especially if you're not using your pool every day, when you do test your chemicals, you should test them all.
And like anything else, the more you test your water, the easier it will be to maintain. Especially when your TA is properly balanced. Your water will become significantly easier to manage and you'll use less Chlorine and Acid. Your Chlorine will also consistently be more effective and keep the water cleaner.
One of the tell signs that your Alkalinity is off, is if you're constantly adding acid. This is one of the ways we would monitor chemical consumption at Pool Rangers, Inc. If we noticed at the end of the month, that an employee had higher than normal acid purchases from our Distributor - especially compared to the rest of the employees. We would know that he wasn't managing his chemicals properly and that the TA in his pools was most likely the cause. So we'd have to go take some water tests and rectify the issue.
Alkaline compounds in the water such as bicarbonates or baking soda, carbonates, and hydroxides remove H+ ions and lower the acidity of the water which means they also increase pH. They usually do this by combining with the H+ ions to make new compounds. These are sometimes referred to as "Alkalinity up" or "increasers." The two most common are Sodium Bicarbonate (NaHC03) or Sodium Carbonate (Na2CO3) otherwise knows as "Soda Ash." Approximately 1.5 pounds of sodium bicarb will increase 10,000 gallons of water by 10 ppm.
To reduce Total Alkalinity, acids like Muriatic Acid or Sodium Bisulfate is added to the water. Approximately 2.1 pounds of sodium bisulfate or 1.6 pints of muriatic acid will reduce the total alkalinity of 10,000 gallons of water by 10 ppm. Make sure not to add more than 1 gallon of acid per 10,000 gallons of water. If your pH is too high or alkaline you can also lower it by injecting carbon dioxide or CO2 into the water which has become more popular in commercial applications. This also raises TA.