We usually focus on indoor swimming pools on this blog, but a recent article by the Guardian provides an opportunity to take a look at some of the best seawater pools in Europe. No chlorine, pH correction, dilution, circulation, filtration, coagulation or heating required.
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Apparently, an operator added hydrogen peroxide to the Rio Olympic Pool. The rationale behind the decision to add this chemical is not clear. It could have been intentional, as hydrogen peroxide is used in some swimming pools as an oxidiser. The problem is that the chemical is also used as a chlorine neutraliser. So when the hydrogen peroxide was added, it went to work and promptly neutralised all of the chlorine thus allowing organic plant life to thrive, since it now had water, sunlight, nu...
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It may be necessary to decrease the levels of chlorine on occasion and certainly following superchlorination. If you are going to be dumping a significant quality of swimming pool water for any reason, there would usually be a requirement to let the local water authority know and they would almost certainly require you to eliminate all traces of chlorine from the water before they granted permission to discharge (chlorine is harmful to aquatic organisms).

In normal operations, it would usual...

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Following on from our previous post regarding hand-dosing of chlorine, here is some guidance on superchlorination.

Superchlorination is not recommended as a routine or even occasional method of shock dosing to compensate for inadequacies in pool treatment. It is generally bad practice, and can generate unwelcome by-products. But if something has gone wrong – poor results from microbiological testing perhaps, or a catastrophic breakdown in treatment – it may be necessary to superchlorinate....

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Sometimes there will arise a need to introduce chemicals into the pool manually (hand-dosing). This is a potential hazardous activity and should not be performed by people who have not received the appropriate level of training.

General Procedures

• Always wear the appropriate PPE.

• Always add the chemical to the water, NEVER add water to the chemical.

• NEVER mix a chemical with another chemical. Only ever mix with water.

• Never hand-dose chemicals into the swimming pool when occupied.

â...

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This week, the Royal Life Saving Society published a news article concerning the risk of drowning via suction entrapment in hot tubs.

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Swimming pool operators ought to be aware that it is possible to create highly toxic gaseous chemical substances if something goes wrong in the plant room. For example: mixing calcium hypochlorite (an alkaline substance that contains chlorine) with an acidic substance (like sodium bisulphate - which is commonly referred to as dry 'dry acid') will result in a reaction that will produce chlorine gas.

The above scenario may happen because an operator inadvertently introduces a chemical into the i...
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pH stands for the 'power of hydrogen' and is a critical factor in the treatment of pool water. The recommended range for the pH level to be maintained at is 7.2 - 7.4. The reason that the pH level needs to be kept between these values is that the disinfection efficiency of the chlorine  falls off significantly at higher pH levels and the coagulant will also not be as effective. At lower pH values, the pool water will be too corrosive.

The effect of the pH level on the disinfection process is a...
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If you suspect your pool has a leak, but need to know for sure, you can find out very easily by using the 'bucket-test'. Put some pool water in a bucket and then put the bucket in the pool on the top step. Get it so the level of the pool water is exactly level with the water in the bucket. Leave it for a couple of days and then compare the water levels. If there is a leek, the level of the pool water will be lower than the water level in the bucket.
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Cryptosporidia is a parasite that is of particular concern for pool plant operators because it is not killed by chlorine. The parasites live inside a protective shell called an oocyst which protect them from the chlorine in the swimming pool or spa water. If these oocysts are ingested by swallowing contaminated water, the cryptosporidia with hatch out of the shells and reproduce, causing a gastro-intestinal illness. When the newly-created oocysts are expelled from the body via the faeces, the...
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Sodium Hypochlorite is the chlorine disinfectant most commonly used in UK swimming pools. It's supplied in liquid form and is similar in appearance to household bleach, which itself contains approximately 5% Sodium Hypochlorite. It is possible to produce Sodium Hypochlorite on-site by passing an electrical charge through a solution of Sodium Chloride (salt water).

 

The benefits of this type of system are that there is no direct handling of hypochlorite chemicals and there will be reduced amoun...
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In many areas of management (and life in general), there are a limited number of issues and concerns that have the most impact on whatever it is your trying to manage. Effective swimming pool water treatment and pool plant operation is no different. During one of our pool plant courses, you will learn all sorts of things in order to understand what's happening with the swimming pool water and be able to diagnose and rectify problems quickly. 

All sorts of things can go wrong with swimming pool...
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A pool that is 25 metres long, 12 metres wide, with an average depth of 1.5 metres will hold 450 cubic metres of water. If there are, say, 30 people in the pool, each of them will have 15 cubic metres of water each.

Contrast this situation with a spa pool. A spa will only hold about 3 - 10 cubic metres of water, depending on the type. Let's say we have a spa pool that holds 5 cubic metres and has 10 people in it. Each person now has only half of one cubic metre of water each.

Even though there ...
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A few people struggle to fully understand the concept of what is known as 'breakpoint chlorination' during the pool plant operators course. In basic terms, as far as pool plant operators are concerned, breakpoint chlorination describes the point at which there is twice the amount of free chlorine than combined chlorine.

Imagine a swimming pool that has high levels of pollution. If you were to introduce some much-needed chlorine into the pool, it would quickly end up as combined chlorine as it ...
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Energy is used when increasing the temperature of something. Heat is transferred from something hot to something cool.This heat is called 'sensible heat'. Energy is also used when a change takes place in the state of something. For example, when liquid water turns into water vapour. 

Both of these forms of heat are used to achieve energy efficiencies in some air handling systems for swimming pool halls. In order to provide a healthy and comfortable environment for bathers, spectators and staff...
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This article aims to provide a worked example of a PPE assessment for the routine task of filling up the chlorine day tank with calcium hypochlorite granules. Please note that the assessment does not cover issues relating to chlorine gas and therefore, a separate assessment would need to be carried out for this.

• Download (free) HSG53 - Respiratory Protective Equipment at Work.
• Get the MSDS sheet for the substance in question (go here for calcium hypochlorite MSDS).
• Work through the steps. There ...

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If you have the filter manufacturers instructions, refer to those as they will inform you of how often a backwash needs to take place. Quite often though, these instructions have been lost long ago, so this article will outline some recommendations. What happens to a filter over time is that as it does its job and collects within it all the pollution and contaminants that you don't want getting in your pool, it becomes blocked up. This process is actually helpful towards the beginning of the ...
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Backwashing is the process of cleaning the filters. Consider that the job of the filters is to trap as much of the various types of pollution as possible and you will appreciate that over time, more and more of this pollution will build up within the filter media. At regular intervals, this accumulated pollution needs to be gotten rid of. The method is to reverse the flow of water through the filter, so instead of water going in at the top and coming out at the bottom, the water goes in at th...
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For the purposes of pool plant operation, chlorinated isocyanurates (also referred to as stabilised chlorine) can be thought of as a combination of cyanuric acid and chlorine. Why would a pool plant operator want cyanuric acid in addition to just chlorine? The answer is because in outdoor pools that are exposed to sunlight, the chlorine will get diminished by the UV in the sunlight. It needs an additional chemical to be added to prevent this from happening. This chemical is cyanuric acid. It ...
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Cyanuric acid is mostly used in outdoor pools. The reason for this is that chlorine is broken down by ultra violet light. Sunlight contains ultra violet light and when the sun shines onto an outdoor pool the chlorine gets depleted very quickly. The pool plant operator needs a way of 'stabilising' the chlorine and that's where cyanuric acid comes in. Cyanuric acid binds with the hypochlorous acid (the disinfectant in chlorine) and makes it more resistant to degradation by UV. The drawback is t...
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Although this video is about the treatment of potable water treatment, many of the processes involved are very similar to the treatment of swimming pool water. In terms of pool plant operation, it's worth a look:


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Excess physical pollution floating on the surface of the swimming pool can sometimes cause a problem for pool plant operators. The heavier physical pollution sinks to the bottom, but the lighter stuff remains floating around on the surface and looks extremely off-putting to pool users. This type pollution usually consists of things like; bits of float, plasters, hair etc. There will also be chemical pollution sitting on or around the surface of the pool, stuff like; biofilm, grease, sweat, mu...
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Bromine is a disinfectant that works in a similar way to chlorine, in that it oxidises pollution on contact. The active disinfectant produced by the addition of chlorine-based disinfectants is hypochlorous acid, whereas the active disinfectant produced by the addition of bromine-based disinfectants is hypobromous acid.

Bromine-based disinfectants are not widely used in conventional commercial pools, largely because it is known to sometimes cause a condition known as ‘bromine itch’ in so...

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Ultra violet disinfection is a process whereby the swimming pool water flows through a UV chamber and is exposed to UV light. The UV light is harmful to bacteria and other micro-organisms because it mutates the DNA of the organism, which means that it can no longer reproduce. The UV chamber is installed in the plant room and once the swimming pool water has passed through the chamber, it will have been purified to the extent that any chlorine in the water will have also been removed. UV disin...
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Ozone is a disinfection method that uses ozone to oxidise contamination in the pool water. It is a more powerful oxidiser than chlorine and will actually oxidise (and therefore, remove) chlorine from the pool water when it passes through the ozone dosing system. It is a non-residual disinfectant, which means that no ozone remains in the pool water once it has passed through the ozone dosing system in the plant room. This is different to chlorine because under normal circumstances, there will ...
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Balanced water testing is something that you should be doing weekly in order to determined whether you pool water is 'balanced'. This refers to whether the water is corrosive or scale-forming.

Corrosive water will eat away at grout, pump seals, pipework etc. (basically, anything it comes into contact with). Scale-forming water does the opposite of corrosive and instead of eating away at things it will form a scale on it (you're likely to see the effect of this on the heating element of your ke...
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Alkalinity is the amount of alkaline salts (carbonates, bicarbonates and hydroxide ions) present in the pool water. It is an important factor in the treatment of swimming pool water because it acts as a pH buffer. If your alkalinity levels are too low, you may find it difficult to control the pH level; when you add and acid, the pH level will drop too fast, then when you try to correct the problem, the pH level will shoot up past the level you want it at. If your alkalinity levels are too hig...
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One of the main problems for many swimming pools is condensation. Condensation happens when the water vapour in the air condenses into liquid water and forms a film on surfaces. This will then start to attack the fabric of the building and lead to expensive repair bills further down the road. For the pool operator, the objective is to keep this condensation to a minimum. This can be achieved by being aware of the temperature at which the water vapour in the air will condense into liquid water...
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Straining is one of the processes taking place during filtration and is perhaps, the one most pool operators will be familiar with. The process involves dirty water passing through the filter media (usually sand) and particles of pollution becoming trapped in the small gaps (pores) between the grains of sand because they are too large to pass through.

Take a look at the picture (click to enlarge). In swimming pool filters, the size of the sand grains is usually 0.5 - 1.0mm. This results in a p...
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The filtration rate is the rate (in metres per hour) at which the pool water moves down through the filter during normal operation. It is not to be confused with the circulation rate, which is the rate (in cubic metres per hour) at which water is moving through the circulation system.

The filtration rate is calculated by dividing the circulation rate by the surface area of the filter. For example:

Circulation Rate: 100 cubic meres per hour
Filter Surface Area: 5.72 metres squared
Filtration Rate:...
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Physical pollution is one of the three main categories of pollution that concerns pool plant operators (the other two being chemical and biological). As you might expect, physical pollution is made up of stuff that does not dissolve into the water:

• dirt 
• grit
• sand
• plasters 
• bits of float  

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Free chlorine is measured with the DPD1 test. It indicates how much of the total chlorine in the pool has not yet reacted with any pollution (ie, combined) and is therefore free and available to carry out it's purpose as a disinfectant.

There should always be enough free chlorine in the pool to minimise the risk of cross-contamination. The minimum recommended amount is 0.5mg/l. any less than this and you will need to shut the pool. The maximum recommended amount is 2.5mg/l. There is no need to...
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Every month, all public pools should be tested for bacteriological water quality by a UKAS accredited laboratory. These tests serve as a link of 'health check' and will give the pool operator an indication of the performance of the swimming pool plant system. There are four different tests that are carried out:

Aerobic colony count

Total coliforms

Escherichia coli

Pseudomonas aeruginosa

Aerobic Colony Count
The first test, aerobic colony count, is a test for the number of bacteria in the sample of ...
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Sedimentation is one of the processes that is taking place during filtration, the other two being straining and adsorption. Fine particulate matter settles on the upward-facing surfaces of the sand grains. The process of sedimentation can remove finer particles of pollution than straining. As the amount of sediment increases, the amount of space in between sand grains (pores) decreases. This will cause the velocity of water through the filter to increase. Further sedimentation can then no lon...
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Adsorption is one of the processes taking place during filtration, the other two being straining and sedimentation. It is not to be confused with absorption. With adsorption, very small particles of pollution adhere to the surface of the sand grains. This process is promoted by electrostatic charges within the particles (similar to a balloon 'sticking' to a wall). Once particles begin to adhere to the sand grains, a sticky coating builds up, which promotes further adherence of particles onto ...
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Coagulation is an important process in the swimming pool water treatment process. It helps to remove very small particles from the pool water. In a conventional swimming pool sand filter, the size of the gaps between the sand grains (pores) are around 70 microns. As the filter begins to trap particles, the size of the pores decreases. This is known as 'filter ripening'. When the filter is fully ripened, it will be capable of trapping particles the size of around 5 - 10 microns. The size of cr...
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Source water refers to where the mains water that supplies your swimming pool comes from. The water companies collect water from a variety of sources. Some of it is collected from ground waters such as wells and boreholes etc., and some of it is collected from surface waters such as lakes, rivers, streams etc. The ground waters have a higher content of calcium carbonate and are known as 'hard' water. The surface waters don't have such a high calcium carbonate content because they haven't perm...
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Cryptosporidia is an organism that pool operators need to be particularly aware of. The main problem with it is that the chlorine in the pool water will not kill it due to the fact that it is protected within a shell that the chlorine will not penetrate. Cryptosporidia causes an acute gastro-intestinal illness and is introduced into the pool water via faecal contamination. If someone has an accident in the pool and the result is a loose, as opposed to solid stool, you as pool operator are goi...
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Oxidation is a process that has a disinfecting effect on swimming pool water pollution. It's basically a reaction between the oxidiser (the chlorine for example) and the pollution. The oxidiser will take electrons from the pollutant substances in the water, which breaks down and kills them. It's a very similar process to combustion (burning) and rusting. You can also observe the process if you peel an apple and see brown areas start to appear after a while (if you don't eat it, that is). What...
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If you've ever seen a swimming pool being emptied, you will have noticed that as the volume of water decreases, so does the 'blueness' of the water. Why is this? Well, basically, water absorbs light. You probably already know that light at wavelengths that are visible to humans is made up of the seven colours of the spectrum, ie. Red, Orange, Yellow, Green, Blue, Indigo, Violet. Water absorbs light at shorter wavelengths first, so the red gets absorbed and is therefore not visible. The blue i...
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If your total alkalinity levels are too high, or too low; you will have problems controlling the pH levels. High total alkalinity causes 'pH lock', low total alkalinity causes 'pH bounce'. 

As pool plant operators, we all know that the pH of the swimming pool water is a critical factor. If the pH is too high, the disinfectant properties of the chlorine will be minimised. If the pH is too low, the swimming pool water will be too corrosive. Controlling the pH levels is usually a simple process w...
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If you carry out your weekly pool water balance test and find that the total alkalinity levels are low, you're going to need to add some sodium bicarbonate. This chemical will introduce some alkalinity into your pool without having too much of an effect on the pH level. The sodium bicarbonate that you add will go through various chemical reactions and some of it will convert into different chemicals according to what the pH level is at any given time. If the pH is high, some of the sodium bic...
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