Shock Treating/ Super Chlorinating

"Burning up the pollutants with strong oxidizing chemicals"

Shock treating or shocking refers to the addition of anything to the water that will remove or destroy ammonia and nitrogen compounds by oxidation - traditionally this has been chlorine. There are now some non-chlorine shock products.

Organic matter and ammonia compounds enter a swimming pool or spa from many sources. Swimmers and bathers are major contributors with their bodies giving off saliva, sweat, urine and faecal matter. Windblown dust, fertilizers, algae, leaves, twigs, certain water-treatment chemicals and rain introduce contaminants into the water.

Chlorine and bromine combine with ammonia and nitrogen compounds to form amines. Chloramines smell bad, they are eye and body irritants and they are also poor disinfectants. Bromamines do not have an odor problem and are as effective as free bromine for disinfection. Organic wastes build up and become sources of irritation.

Dealing with the problem of combined chlorine requires testing the water to see how much of the chlorine in the water is free and how much is combined. The commonly used OTO test will not perform this task. It can only tell you the total chlorine level and can't differentiate between free and combined chlorine. However, a DPD test kit or a syringaldazine test strip will do the job.

Chlorine Reacts with Ammonia to remove it.

When chlorine is introduced into swimming pool or spa water it forms hypochlorous acid (HOCl (free chlorine)) which dissociates into H+ and OCl-, the degree of dissociation depends upon the pH. The OCl- is a strong oxidizer and will oxidize the ammonia to form a combined chlorine compound known as monochloramine (NH2Cl and OH. More chlorine as OCl- is required to continue the oxidation of the nitrogen or ammonia. If no more chlorine was in the pool or added to it, the pool or spa water would have a large amount of combined chlorine as monochloramine rather than the desired free chlorine.

As more chlorine is added, the monochloramine is now oxidized by the additional chlorine as OCl-) to form dichloramine (NHCl2 + another OH-). The dichloramine is again oxidized by OCl- to form trichloramine (NCl3 + another OH-). The trichloramine is unstable and breaks down to simple nitrogen and chlorine completing breakpoint chlorination.

Superchlorination to truly achieve the destruction of all organic waste can be very tricky. If not enough chlorine is added, the combined chlorine problem is only made worse. When this happens, eye burn and skin irritation are 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.

It takes 7.6 parts by weight of chlorine to oxidize 1 part of ammonia. Other organics or products in the water will also consume some of the added chlorine so that 7.6 parts is not enough. 10 parts of chlorine for each part of ammonia is generally the required amount. Dirty and contaminated pools could take up to 25 parts or more of chlorine. As a general rule of thumb, the addition of 10 times the combined chlorine level will achieve breakpoint. In other words, if the water has 0.5ppm of combined chlorine by test, you will need to add 5ppm or more of chlorine.

Each of the popular chlorine products provide a different amount of available chlorine when added to water. In a typical 100,000 liter pool it will take about 1 kg of available chlorine to achieve 10 parts per million.

Using the chlorine conversion chart, you can find just how much of each type of chlorine will be required to provide this amount.

One problem that has always existed with superchlorination is that if you do not add enough chlorine to the water to achieve breakpoint, you make the problem worse, because all you have done is increase the level of combined chlorine. If you add too much chlorine, you will not only reach breakpoint, but you will also make so much excess free chlorine that swimming will need to be discontinued until the free chlorine residual drops to a safe level for swimmers (less than 5ppm). In an indoor pool, this could take several days and could have a major financial impact on a commercial pool, where lost swimming time means lost revenue. Several of the disadvantages of using chlorine as a shock treatment are overcome by the use of non-chlorine shocks. [Go to top]

Non-Chlorine Shock

The active ingredient in these non-chlorine shock products is potassium peroxymonosulfate, also known as permonosulfate. Like chlorine, permonosulfate is an oxidizer that will destroy organic contaminants such as ammonia in swimming pools and spas. However, permonosulfate compounds do not kill or disinfect they simply control organics and combined chlorine, helping assure that the chlorine can do its job as a sanitizer. Permonosulfates oxidize by using the element from which oxidation derives its name -- oxygen. Oxygen is a pure form of oxidizer. Unlike superchlorination which is used to destroy problems such as odors, eye and skin irritation after they occur -- Permonosulfates are effective in preventing these problems because permonosulfates do not contain chlorine, but rather oxidize waste through the use of oxygen, they do not go through the various stages of chloramine formation to achieve breakpoint. Instead, they react directly with the ammonia to produce chloride and nitrogen. No matter how little of the non-chlorine shock you add, at least some of the organic contaminants will be destroyed, and no additional chloramines will be formed. This overcomes one major drawback of superchlorination. And if you overdose with a non-chlorine shock by adding more than is required, no extended waiting period is needed before swimming can be resumed. Although bathers should not be present when any chemical is added to the water, swimming can be resumed after the permonosulfate has had a chance to dissipate, usually just a few minutes. In fact, the excess chemical will remain in the water, ready to destroy any contaminants that may enter the pool from bather waste and other sources.

Permonosulfates are 100-percent soluble and will not leave a residue or bleach vinyl liners or swimming suits. Because they are chlorine-based, it is not necessary to calculate how much to add to beat a given chloramine problem. Permonosulfates help prevent chloramines from forming, so whatever quantity is applied will have some positive result. Unlike superchlorination, which requires you to figure out how much chlorine to add and how often to correct problems, permonosulfates, are generally added at the rate of 1 pound per 10,000 gallons on a regular, weekly basis.

Permonosulfates effectively control the formation of chloramines, which cause odors, reduce disinfection and cause eye and skin irritation. Permonosulfates cause an acidic condition to occur ie.they have a low pH of about 2.3 to 3, so steps will need to be taken to counteract the acidic condition that may be caused by using them. Permonosulfates do not add to the calcium or other undesirable solids or cyanuric acid in the water. Also, no special handling is required, and there is no reason to close the pool or spa or to restrict swimming due to excessive chlorine residuals. Finally. there is no need to calculate how much to add in order to be effective.
Permonosulfates are also safer to store and handle than chlorine products, because they will not burn or release chlorine gas. [Go to top]

Prepared by Trevor Croll,

42 Pearse Street, Keperra, Queensland Australia, 4054.
Phone 61 7 3855 1115