by Joe Sweazy
Derived from Pool&Spa Marketing June 2006

Monopersulfate is a non-chlorine shock treatment often used by spa owners because it requires only a short waiting period before bathers can re-enter the water. It also cuts down on the odor and irritation caused by elevated levels of chlorine. Monopersulfate is being used more frequently today, primarily due to the rising popularity of mineral purification systems.

Using Monopersulfate With Chlorine - Chlorine is by far and away the most popular sanitizer used by pool and spa owners because of its ability to quickly and effectively sanitize pathogenic (disease-causing) bacteria and viruses. Surprisingly, only 10 per cent of the chlorine added to spa water goes on to kill living organisms. The other 90 per cent of the chlorine oxidizes (destroys) waste products in the water, such as sweat, skin particles, and sun screen introduced into the water by bathers. Chlorine also has to oxidize dust, bugs or grass, which always seem to find their way into the water all by themselves.

The byproducts of chlorine oxidation are chloramines, also known as combined chlorine. Chloramines have a very strong chlorine odor, and they cause nasal and eye irritation. Shocking the water with chlorine will eliminate excessive chloramines, but it requires raising the spa chlorine level to approximately 10 ppm. After superchlorinating the water, bathers must wait until the chlorine residual comes down to the acceptable range, between 1 ppm and 5 ppm, before getting back in the water. This can take hours, depending on how high the chlorine level gets. It is difficult to add just the right amount and the higher the level gets, the longer bathers will have to wait to get in.

Monopersulfate can eliminate wastes in a spa without the unpleasant side effects of chlorine. While it cannot effectively sanitize (kill bacteria) in a spa, monopersulfate can be used to shock the water. This allows bathers to return to the water sooner - typically less than 30 minutes after the monopersulfate shock has been added to the water. Monopersulfate eliminates impurities through oxidation, conserving the chlorine residual for killing bacteria Best of all, monopersulfate does not leave behind any irritating or unpleasant byproducts when it oxidizes wastes.

Using Monopersulfate With Bromine - Another popular choice for sanitation in spas is bromine; This is a good alternative to chlorine because it is more stable in hot water, does not produce the same strong chlorine odor, and is still an effective sanitizer in the combined bromamine state. For this reason, most bromine test kits measure total bromine instead of free bromine. The one drawback to bromine is that it tends to be slightly more expensive than chlorine.

Monopersulfate in a bromine system is used as an activator for the bromine that has been used up and converted into a non-active form. Monopersulfate performs some oxidation of waste as in the chlorine system, but it is also capable of reactivating the bromine so that it is once again capable of sanitation and oxidation. Chlorine is not capable of this type of reactivation. Therefore, monopersulfate tends to increase the bromine level in spas when it is added to an established bromine system.

Again the unique advantage of the monopersulfate shock is that bathers can se-enter the water a short time after the shock has been added - typically less than 30 minutes after the monopersulfate shock has been added to the water.

Monopersulfate With Mineral Purification Systems - Because of the unpleasant odor and irritation associated with chlorine, mineral purification systems and other alternate methods of sanitation have been growing in popularity. These systems use dissolved minerals such as copper (to kill algae) and silver (to kill bacteria). While these minerals can keep the spa safe from pathogenic organisms, minerals are incapable of oxidation, so a monopersulfate residual is maintained in the mineral purification systems to oxidize wastes and debris. (In the presence of high levels of chlorine or bromine, monopersulfate dissipates very quickly. In mineral purification systems, where the level of chlorine or bromine is lower, the monopersulfate residual level will stay in place much longer).

Testing Monopersulfate - Monopersulfate needs to be measured after each use, especially if it is being used as the primary shocking agent. This ensures proper oxidation of wastes, yielding clear water for bather enjoyment.

There are few kits available to test for monopersulfate. Almost all testing methods have chlorine interference, meaning that the chlorine level interferes with the monopersulfate test results. These tests actually depend on oxidation of an indicator by monopersulfate. Since chlorine is also a strong oxidizer, it usually causes false positive results in monopersulfate tests.

A subtractive testing method, however, will.provide an accurate monopersulfate value even in the presence of chlorine. First, it registers the total oxidizer value by a chemistry that detects both chlorine and monopersulfate. Second, the use1 completes a test that detects chlorine but not monopersulfate. The difference between the first value and the second value is the monopersulfate value.

Oxygen Shock:
Superchlorination alternative
By Doug Walsh (from Service Industry News)

While alternative methods are gaining in popularity and acceptance, chlorine remains far and away the No. 1 sanitizer used in pools and spas.

Its time-tested ability to quickly kill nearly every microorganism that can cause disease is well known, disinfecting pool and spa water by killing pathogenic bacteria and viruses within seconds of application.

In addition to its sanitizing capabilities, chlorine is also widely used as an oxidizer, helping to rid the water of contamination that can be introduced from a variety of sources. These are generally recognized as bather wastes like urine and perspiration, cosmetic products, sunscreens and lotion. But they also include organic contaminants that can be introduced through wind and rain, such as dust, dirt, pollen, insects, plant and grass debris and airborne pollutants.

The sanitizer works hard at oxidizing or burning up these contaminants, but as they build up in the pool water, they combine with the sanitizer in the water to produce what we call chloramines or bromamines.

In the case of chloramines, they can cause a foul smell and can lead to cloudy, dull water. While still a killing forn of sanitizer, the effectiveness of this combined form of chlorine is minimized and, if left unattended, can lead to poorer and poorer water quality and algae headaches.

One of the problems that occurs automatically is that when these contaminants are introduced into the water, the sanitizer which should be working on killing bacteria and virus shifts and tries to do its secondary job as an oxidizer. Chemically, we say that there is a sanitizer demand.

Unfortunately, as the sanitizer is called upon to oxidize to destroy organic contaminants, its efficiency as a disinfectant is significantly reduced.

To overcome the buildup of the combined forms of sanitizer, the industry standard has been to superchlorinate or shock the water. In this process, the chlorine level is raised to about 10 times the normal readings on a chemical test to reach what is, called breakpoint.

At this point, the chloramines are broken down, bringing the chlorine back to its free and best killing form.

It is common, however, for a small amount of combined chlorine to remain in the water after a corrective breakpoint has been reached, especially when organic nitrogen compounds are present in the pool water. Also in the real world chlorine will continue to combine with contaminants that constantly enter the water, and almost immediately again begin forming chloramines. So realistically, you can never totally rid the water of chloramines.

Another common problem, of course, is finding the proper level of chlorine you must add to reach this breakpoint. As you add chlorine, you are effectively raising he chloramine level even higher and higher in the pool. And if you fail to reach breakpoint, you are simply increasing the undesirable effects.

Also, high chlorine levels in the pool can cause significant down time while normal levels are returned, or you may need to revisit the pool to dechlorinate.

What's a pool pro to do?

One way that pool operators are be ginning to overcome the problem is through use of a non-chlorine shock most notably potassium monopersulfate to shock their pools. And rather than waiting for combined chlorine readings to rise above proper levels, they are using monopersulfates on a regular basis as a preventative measure to oxidize contaminants before they combine to cause water quality problems.

In addition to potassium monopersulfate, other oxygen-based shocking chemicals could include sodium persulfate, sodium carbonate peroxyhydrate (also known as sodium percarbonate) and hydrogen peroxide. Sodium persulfate has about the same active oxygen content as potassium monopersulfate, but has a low reactivity and also can cause a chemical buildup in indoor pools. The other two have high active oxygen content and are commonly used in dechlorination.

The advantages to oxidation without chlorine include that fact that there is no added production of chloramines and sanitizer efficiency is increased without raising the chlorine level. The chlorine without its added duty as an oxidizer is free to do its job as a bacteria killer. At the same time, monopersulfates accelerate chloramine degradation.

With regular, preventative use, you end up with better water quality, longer periods of uninterrupted swim time, and a more manageable maintenance schedule.

Potassium monopersulfate is a strong, odorless, oxygen-based oxidizer that works well with sanitized chlorine, bromine and most alternatives. Unaffected by UV degradation, non-chlorine shock can be added to pool water day or night, and swimming can resume after just a short waiting period.

The product is fast dissolving, and when broadcast uniformly over the water with the circulation system running, it will quickly mix into solution with the pool water. Because of its characteristics, monopersulfates will not damage or fade vinyl liners.

Recommended doses are one pound per 10,000 gallons of pool water, but more frequent and higher doses may be useful in commercial pool applications. In spas, manufacturers recommend oxidizing with non-chlorine shock after each use. Recommended dosage for spas is 1-2 ounces per 250 gallons.

DuPont, the manufacturer of potassium monopersulfate, recommends its use on a regular basis rather than waiting for problems to occur. Their reasoning is simple: If the condition of your pool water is so bad that it needs shocking, something has already gone amiss. And you don't have to be a chemist to know that it makes more sense to prevent a problem in the first place that it does to try to fix one once it has occurred.

The rationale of using this preventative medicine for your customers' pools is a strong one. When the quality of water deteriorates to such a degree that shocking becomes necessary, are you really sure that you are providing enough sanitation?

And during the time you are superchlorinating, your pools may be unusable, which can be especially troublesome in commercial pools. In addition, the work associated with corrective action can be significantly more time consuming than the few minutes added to your routine maintenance schedule to add non-chlorine shock on a regular basis.

When winterizing using a non-chlorine shock can help to prolong the sanitizer residual, which can be a benefit as the pool remains idle for several months on end. The shock treatment accomplishes this by oxidizing wastes and thus "freeing up" the chlorine or bromine to do its job as a disinfectant. Potassium monopersulfate does not, however, kill bacteria and cannot replace your choice of sanitized. And because of its acidic nature, regular use will also lower pH and total alkalinity. Soda ash or bicarbonate should be added to maintain acceptable levels of pH and alkalinity.

When testing, you should be aware that while no interference will be detected when using OTO test kits, there is minimal interference with free chlorine readings on DPD tests. The DPD reacts with the potassium in the total chlorine test to give a false high combined chlorine reading, but there are test kits available to eliminate monopersulfate interference.

When using test strips, service professional should be aware that while there is no interference with free chlorine readings, the potassium can react with total chlorine and total bromine tests.

Monopersulfate compounds even when used on a regular basis as part of a prevention program are not a cure all for water problems. Naturally, you still need to consider: Circulation your pumps and filters should be properly sized for adequate flow and turnover rates.

Condition of the filter elements and media needs to be properly maintained to assure maximum effectiveness.

Regular vacuuming to prevent the buildup of particles that make the water cloudy.

Water balance Are pH, alkalinity or calcium hardness levels too high? These situations can lead to cloudy water problems.

With these considerations addressed and problems persisting, may need to consider addition of water clarifiers or other preventative specialty chemicals to maximize water quality.

But routine shocking to allow sufficient free available sanitizer and minimize the problems taht can develop with combined forms of chlorine or bromine can go a long way to controlling problems before occur.

Shock Treatment:
The Why & How of Superchlorination
By David Dickman (from Service Industry News)

How's this for a bit of misinformation: "Every once in a while, you've got to shock the pool water by adding an extra-large amount of chlorine to get rid of algae and other contaminants that might otherwise be left to grow."

This is an actual bit of advice that was overheard being given to a pool owner by the counterperson at a home-supply store that happened to sell pool chemicals -- and as advice goes, it's dead wrong!

True, you do have to periodically shock pool or spa water. And true, it is often done with chlorine -- although "an extra-large amount" is not really an accurate guideline to be followed.

But the reason given for shocking is the most inaccurate portiion of a generally inaccurate statement. Shocking the water may, indeed, help prevent the spread of algae, but the true purpose of this periodic treatment is to rid the water of organic compounds that irritate swimmers and bathers and tie up chlorine to prevent it from performing its task as a sanitizer.

Yet the notion persists throughout many corners of the pool and spa industry that occasional, "super" doses of chlorine are necessary, but the exact reason for this is as much a matter of custom and tradition as it is a matter of scientifically based water chemistry.

As a pool service professional, it's your job to understand the true reasons for doing what it is you do to treat water. And you also should be prepared to explain your practices to your customers.

And for this, you need a thorough knowledge of shock treatment -- the hows, whys and wherefores of this often misunderstood practice.

For years, operators of public swimming pools have heard swimmers complain that "there's too much chlorine in the water," when, in fact, the problem was too little chlorine.

The most noticeable symptom of this condition is the odor -- that obnoxious "chlorine" smell that assails you the moment you get near the pool -- especially in a heavily used indoor public pool.

Then, once in the water, you are attacked by the other symptoms of the condition: red eyes and sore nose. And if, like most of the public, you are unaware of the way chlorine works to sanitize water, you are drawn to the inescapable conclusion that too much chlorine is to blame.

Yet if you open up a gallon jug of chlorine bleach or pool chlorine and take a whiff, it smells rather fresh and clean -- nothing like the dreadful aroma that attacks you in that public pool. From this alone, it should be obvious that something other than chlorine is the culprit behind that sore nose, those red eyes and that awful smell.

And, indeed, something else is to blame.

You can call it chloramine; or combined chlorine; or organic contamination; or bather waste -- the fact is that an improperly sanitized pool contains irritating levels of chemical compounds that need to be removed before they become a problem.

When a chlorine compound is added to swimming pool or spa water, it reacts with water to form the compounds known as hypochlorous acid and hypochlorite ion. Together, these compounds are known as "free available chlorine" or "free chlorine."

The primary reason for adding chlorine to swimming pool or spa water is to disinfect or kill possibly harmful microorganisms. But once the free chlorine has joined with ammonia and nitrogen compounds to form combined chlorine, its ability to disinfect is hindered. It actually takes 25 parts of combined chlorine to do the work of 1 part of free chlorine.

Ridding the water of chloramines is a 3-step process:

  • Find out exactly how much combined chlorine is in the water.
  • Calculate how much chlorine or shock treatment we need to add to the water to oxidize the combined chlorine.
  • Add the proper amount of chlorine or shock treatment.

First, we need to measure the amount of combined chlorine in the water. To do this, we must use a test kit that can tell the difference between free and combined chlorine. Basically, that means that you must use a DPD kit or a test strip to make your readings -- an OTO test won't give you the information.

Using the DPD test, you first determine the free chlorine level in the water using the DPD #1 tablet. After recording the reading, the DPD #3 tablet is added to the same sample, and the result is recorded. The second reading is the total chlorine level in the water. If the reading is higher than the free chlorine reading, then the difference between the two represents the level of combined chlorine in the water. If the readings are the same, then no combined chlorine is present. The total chlorine level cannot be less than the free chlorine level.

If you use bromine for disinfection, you still must be concerned with organics. Even though combined bromine is a good disinfectant and does not smell or irritate eyes, it is not as efficient as chlorine in removing organic waste.

And if they are allowed to build up, ammonia-like waste products can still be irritating -- creating such conditions as jock itch or skin rash.

Once you know how much combined chlorine is in the water, you have to add about 10 times that amount of free chlorine to get rid of it.

In other words, it your test reveals that you have 1 ppm of combined chlorine in the water, you will have to add 10 ppm of available chlorine in the water to get rid of it.

The process of breakpoint chlorination or the destruction of organic waste in the water is known as "oxidation."

When chlorine is introduced into swimming pool or spa water containing ammonia, the hypochlorous acid (free chlorine) quickly begins to oxidize the ammonia to form a combined chlorine compound called monochloramine.

As more chlorine is added, the monochloramine is oxidized by the additional chlorine to form dichloramine. As even more free chlorine is added, it attacks or oxidizes the dichloramine to form trichloramine. Finally, as even more free chlorine is added, the trichloramine is broken down or oxidized to simple nitrogen and chloride salt, completing breakpoint chlorination. Any chlorine added after this point will be free chlorine, as long as no new contamination of the pool or spa occurs.

The accompanying chart breakpoint chlorination in a graphic way. Let's discuss each of the points on the curve: First, the addition of chlorine to a pool containing ammonia (1) results in a growing production of combined chlorine (2). Once enough chlorine has been added to oxidize all of the ammonia, the combined chlorine rapidly breaks down (3). At this time, little, if any, chlorine remains in the water, because it has all broken down into nitrogen and chloride (4). Any chlorine added after this point will form free chlorine (5), because there is no ammonia to react with the chlorine now being added.

Superchlorination to truly achieve breakpoint -- the destruction of all organic waste -- can be a very tricky thing to accomplish. If not enough chlorine is added, the combined chlorine problem is only made worse. When this happens, eye burn and skin irritation are not reduced, but rather raised to very high and very irritating levels. If too much chlorine is added, it may take days to drop to safe levels (less than 5 ppm) before bathing can be resumed.

By chemical calculation, chemists know that it takes 7.6 parts of chlorine to oxidize 1 part of ammonia. But a number of other factors will affect that ratio: Other organics or products in the water will consume some of the added chlorine so that 7.6 parts are not enough. To be practical, it is best to add 10 parts of chlorine for each part of ammonia.

The problem is figuring out exactly how much of a given chlorine product you will need to provide that 10-ppm level. Using a pocket calculator, you can do this easily, but you've got to remember that 1 gallon of water weighs 8.34 pounds and that ppm (parts per million) is a weight-to-weight ratio.

We're going to assume that you know how many gallons are in your customers' pools or know how to calculate this figure. Once you know this, you must:

  • Take the number of gallons in the pool and multiply by 8.34. This tells you how many pounds of water is in the pool.
  • Take the number 1,000,000 (a million) and divide it by the answer you got after the first calculation. This tells you how many parts per million that 1 pound of chemicals will represent in that particular pool.
  • Take the number 10 and divide it by the answer you got after the second calculation. This tells you how many pounds of available chlorine you will need to add to get 10 ppm.

For a 10,000-gallon pool, the numbers work like this:

  • 10,000 times 8.34 equals 83,400. There are 83,400 pounds of water in a 10,000-gallon pool.
  • 1,000,000 divided by 83,400 equals 11.99 (which we'll call 12). This means that each pound of chemicals we add to the water will be adding about 12 parts per million.
  • 10 divided by 12 equals .83. So we need to add about 4/5 of a pound of available chlorine to get 10 ppm.

Here's an example with a 15,000-gallon pool:

  • 15,000 times 8.34 equals 125,100. There are 125,100 pounds of water in a 15,000-gallon pool.
  • 1,000,000 divided by 125,100 equals 7.99 (which we'll call 8). This means that each pound of chemicals we add to the water will be adding about 8 parts per million.
  • 10 divided by 8 equals 1.25. So we need to add about 11/4 pounds of available chlorine to get 10 ppm.

And an 18,000-gallon pool:

  • 18,000 times 8.34 equals 150,120. There are 150,120 pounds of water in an 18,000-gallon pool.
  • 1,000,000 divided by 150,120 equals 6.66. This means that each pound of chemicals we add to the water will be adding about 6.7 parts per million.
  • 10 divided by 6.7 equals 1.49 (which we'll call 1.5). This means that we need to add about 11/2 pounds of available chlorine to get 10 ppm.

The only other calculation you need to make is to determine how much of each of the various chlorine compounds you need to add to get the correct amount of available chlorine. To do that, you divide the number of pounds you need by the percentage of available chlorine.

For example, if you need 11/2 pounds of available chlorine, and you're using cal-hypo (65-percent available chlorine), you divide 1.5 by .65, which gives you 2.3 pounds.

If you use liquid chlorine (12-percent available chlorine), you need 1 1/2 gallons, because a gallon of liquid chlorine (sodium hypochlorite) provides almost exactly 1 pound of available chlorine.

By now, you are probably beginning to realize that superchlorination is not a simple matter. To do it right, you cannot simply add "some" chlorine -- you might actually be making the problem worse. You have to calculate the required amount and add the correct dose.

Non-chlorine shock treatments go a long way toward simplifying the process. Using chemical compounds called monopersulfates, these products oxidize contaminants without going through the mono- di- and trichloramine chemical process. So they can be added on a 1-to-1 ratio: Each pound of product added will oxidize 1 pound of contaminant.

Non-chlorine shocks are a bit more costly than chlorine compounds, but they eliminate much pool downtime because they work rapidly and do not require time to dissipate.

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