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The Swimming Pool Operators

and Owners Resources Pages

Page 3 - Water Testing and Analysis


ON THIS PAGE

  • Why test the pool water?
  • Water testing frequency
  • The different types of test
  • Pool water testing equipment
  • The Photometer
  • Basic testing methods
  • Testing procedure
  • The Comparator
  • The shaker tube
  • The turbidity test tube
  • Testing the chlorine
  • Testing the pH value
  • Testing the total alkalinity
  • Testing the calcium hardness
  • Testing the cyanuric acid
  • Testing the sulphates
  • Testing the chlorides
  • Calculating water balance

DISCLAIMER:- All the information and advice on these web pages is given in good faith and believed correct and accurate, but we cannot be responsible for any form of loss, damage or injury, however caused, through the use of any information or advice detailed here.

COPYRIGHT:- All the information on these pages are for your PERSONAL USE. You may freely download, and retain for your own use anything that appears on this site provided you also retain and include a reference to this site and this copyright notice.. However, any part or whole of any article, text, or information that originates from this site may not be included in any publication, commercial literature, etc., etc., on any other web site, - or in any area where commercial or personal gain is conceived, without the express permission in writing from Malcolm R Bartier.


WHY TEST THE POOL WATER?

Water testing is an essential part of swimming pool operations and maintenance. Chemicals are constantly being added to a swimming pool and spa. Chemical reactions are constantly taking place. Water is constantly evaporating leaving behind a constantly increasing residual chemical concentration. In order to make sure that the water is safe for swimming the wise pool owner or operator makes sure that they regularly carry out a number of simple water tests. The frequency of these tests depends on the type of pool, and the type of chemical residual that is being tested.

Whether the pool has an automatic chemical control system is irrelevant. Automatic chemical control systems can and do go out of calibration. No matter how much money is spent on an automatic chemical control system, it is still essential to carry out regular testing using proper swimming pool water testing equipment.

WATER TESTING FREQUENCY

Busy commercial and public pools will probably be manually testing the pH value, and the Free and Combined Chlorine every 2 hours or even more frequently. Hotel pools, schools, and less busy public pools should be testing at least 5 - 6 times per day.

Despite what many swimming pool salesmen say, - the home pool owner will benefit from testing their pool water at least once a day - more often if the pool is being well used.

Not all the tests need to be carried out each time the water is tested. The essential tests are pH value and Free & Combined Chlorine (assuming chorine is used as the disinfectant)

There are 3 main types of test that need to addressed.

  • (1) Residual disinfectant and disinfectant by-products. - i.e. Free Chlorine and Combined Chlorine

  • (2) Water Balance. - i.e. pH, Total Alkalinity, Calcium Hardness, and Temperature.

  • (3) Undesireable residual chemicals. - i.e. Sulphates, Chlorides, and Cyanurates (if used).

 

The types of test and the frequency depend primarily on the particular chemicals used for disinfection and pH control. But high residuals in the make-up water - such as calcium, total alkalinity or sulphates should also be taken into account.

Cyanurates do not normally occur in tap water so it is only necessary to test for this residual if cyanuric acid is introduced into the pool. This would be through the use of dichlor stabilized chlorine granules, trichlor stabilized chlorine tablets, or if the cyanuric acid powder has been added to the water.

Sulphates are often present in tap water at varying levels. If high levels are already present in the make-up, it is important that the levels in the pool are regularly monitored since evaporation may cause an excessive concentration to build up. If dry acid (sodium bisulphate) is used for pH control, then it is usually essential that the sulphates level is regularly checked.

Chlorides enter pool water from a number of sources. The normal chlorine or bromine disinfection process results in a residual of chlorides, and chlorides will be washed off the skin of bathers (in sweat), but high levels of chlorides will result from the use of sodium hypochlorite (liquid chlorine) and/or hydrochloric (muriatic acid)

Calcium is a naturally occuring residual in water. Like sulphates, if high levels of calcium are already present in the make-up water, it is important that the levels in the pool are regularly monitored since evaporation may cause an excessive concentration to build up.

The Total Alkalinity will vary from area to area. The maintained pH value of the pool water will also have a bearing on the T.A. The use of CO2 gas for pH control will often cause the T.A. to rise, creating a need for regular testing.

The pH of the pool water is the most important test. The pH value of the water determines whether or not the chlorine is effective at disinfection. It determines whether or not the water is corrosive, neutral or scale-forming, and it also determines whether some chemicals can remain in solution or if they crystalize, causing cloudy water.

The chlorine tests, in conjunction with the pH test, will indicate whether the pool is being operated in a safe manner. They also provide a "presumptive" test for common bacteria - i.e. provided that the disinfection has not failed at any time, the operator can be fairly sure that the pool water is bacteriologically safe. This does not remove the responsibility for regular microbiological testing of commercial pools, but provides interim assurance between actual microbiological tests.

There are a considerable number of other tests which are used for analysis purposes, determining the causes of poor quality water.

We regularly carry out up to, or even more than 50 different water chemistry tests, depending on the type of problem we are investigating.

This is where we use our expertise, knowing which trace chemicals to test for, and their interaction with others already present in the pool water.

The chemical tests that we list here above are those which we consider essential and fundemental tests for maintaining quality swimming pool water.


POOL WATER TESTING EQUIPMENT

Simple water Test Kits for the home pool owner.

. Please wait while this image of a Water Test Kit is loaded

There are a number of manufacturers of swimming pool test kits for home use, providing good quality but simple equipment that performs sufficiently accurately.

The Testers on the left are simple pH and Chlorine or pH and Bromine Testers.

The plastic container is filled with pool water, the appropriate tablets are inserted into each compartment and the cover placed in position so the tester can be shaken to dissolve the tablets.

The Test unit is then held up to a good North Daylight and the sample colours compared with the transparent standards attached to the unit.

The Testers on the right are a little more sophisticated. One uses liquid reagents, and usually incorporates a method of determining just how much acid or alkali is required - using and Acid/Alkali Demand test. Total Alkalinity and Calcium Hardness Tests can also usually be carried out. The other uses tablets, and incorporates Total Alkalinity as well as the usual pH and Chlorine tests.

As before, when testing for pH and Chlorine the unit has to be held up to a good North Daylight to compare the coloured samples with the colour standards attached to the unit.


More Comprehensive Water Test Kits for Commercial Use

Please wait while the image of a Comprehensive Test Kit is loading .

These Test Kits (above) are probably typical of the more comprehensive test equipment used by most commercial pools, (and more enthusiastic home pool owners).

These Test Kits consist of a Comparator for accurately determining the pH value and the Chlorine levels, and Titration tubes for Total Alkalinity and Calcium hardness levels.

The Comparator enables a more accurate assessment of Proportional Colour matching. The colour standards are mounted on removable wheels, and the water samples are held in removeable cuvettes (test tubes)

Additional reagents and/or equipment is needed for Cyanurates, Sulphates, and Chlorides tests.

There are a number of manufacturers of swimming pool test kits incorporating comparator and titration methods for water testing.

Comparators can give very accurate results when used correctly, particularly if attached to an electric mains powered artificial Daylight Source.

This ideal set up then gives repeatable and dependable accuracy when used by a trained operator.


IMPORTANT NOTE

Proportional Colour tests CANNOT be accurately achieved using flourescent lighting.

It is essential that either a good North Daylight source, or an Artificial Daylight Source designed for pool water testing is used.

Accurate Water Test results cannot be achieved using poor quality lighting.


Photometer Water Test Kits

This Photometer Test Kit (above) is fairly typical of the compact versions now begining to become popular in commercial and home pools.

The Photometer uses Proportional Colour to determine specific chemical levels but instead of the user comparing the sample colour with a set of Colour Standards, a beam of fixed wavelength light is passed through the coloured sample and the emerging light is analyzed electronicaly The light absorbance factor of the sample water, which is affected by its colour, is calculated and (usually) a display on the instrument give the actual chemical level recorded.

The Photometer is a very accurate machine and by definition it has its own light source, making it independant of daylight or artificial daylight light units. Since the results of the test are automatically displayed on a digital panel, the unit is ideal for use by operators who are colour-blind.

The high accuracy achieved by the Photometer can only be maintained by observing clean and careful working practices. Water splashes, dust and dirt should not be allowed to land on the unit, especially anywhere near the light source and receiver. The test cuvettes must be carefully cleaned and dried after use to prevent staining of the glass.

Most manufactures of Photometers provide special reagent tablets, formulated to the higher accuracy demanded by this instrument.

The Manufacturers, (not the salesmen) of many photometers will often tell you that to get a truly representitive assesment of the water, between 3 to 5 consecutive tests must be taken and their results averaged. We have found from experience that simply taking 1 photometer test does not always give accurate results.


A SIMPLE QUESTION

When a pool owner has just spent many thousands of pounds (or dollars) on a swimming pool, why do they often try to make do with the cheapest and most basic test kit that costs only a few pounds (or dollars) ??

If you have just bought a "state-of-the-Art" Wide screen TV with Dolby surround sound, - would you try to use the cheap aerial/antenna that you take in the camper truck - or even a wire coat-hanger??

The replacement of a vinyl pool liner,or the regrouting of a tiled pool can cost many hundreds of pounds (or dollars). Why do so many home pool owners pay so little attention to water testing. and often use an old, dirty and faded cheap tester - (which is often left lying around on the ground near the pool) and risk damaging the liner through incorrect chemical levels??


BASIC TESTING METHODS

Please Note :- We still prefer using the Comparitor and Daylight Source for water testing. Having solved a lot of 'obscure' water chemistry problems with the Comparitor at facilities where a photometer was used, we find that for 'day to day' water testing, the comparitor plus daylight box gives fast and reliable accuracy which is more than adequate for swimming pool testing.

(The following tests methods and procedures are based on the Comparator, Titration, and Turbidity test methods)

The most popular method for testing for the presence of a particular chemical is based on Colour, and there are two Sub-methods of colour testing.

(A) Proportional Colour tests:-

  • (1) A measured sample of pool water is obtained.
  • (2) A reagent is added to the sample.
  • (3) The action of the reagent and a particular chemical cause the sample to change to a specific colour.
  • (4) The sample colour is then compared with a set of labled colour standards and the nearest match indicates the level of the particular chemical present in the sample.

This type of test is normally used for pH, Free, and Total Chlorine

 

(B) Titration Colour tests:-

  • (1) A measured sample of pool water is obtained.
  • (2) One unit of a reagent is added to the sample, which changes to a particular colour.
  • (3) Additional units of the reagent are subsequently added, one at a time until the sample suddenly changes to a different colour.
  • (4) The number of reagent units is applied to a simple formula to determine the level of the particular chemical in the sample being tested

This type of test is normally used for Total Alkalinity, Calcium Hardness, and Chlorides

 

The next most popular test method is probably turbidity,

  • (1) A measured sample of pool water is obtained.
  • (2) A reagent is added to the sample.
  • (3) The action of the reagent and a particular chemical residual causes the sample to become cloudy in proportion to the level of the particular chemical being tested.
  • The cloudiness is measured in a simple Turbidity Tester and usually a direct reading is obtained giving the level of the chemical being tested..

This type of test is normally used for Cyanuric Acid and Sulphates


TESTING PROCEDURE

Collecting water samples

WARNING:- NO GLASS of ANY KIND may be used for collecting the water sample.

Glass in water has the same refractive index as water, and broken glass becomes completely INVISIBLE in water. Cool glass placed in warm pool water frequently cracks or breaks.

It is highly irresponsible and dangerous to allow glass anywhere near a swimming pool.

Use a CLEAN plastic bottle or container to collect the sample. Rinse it thoroughly with the pool water before taking the sample for testing.

The site chosen for taking the water sample should be continuously used to maintain a standard continuity. Don't take a sample from a different place each time.

The sample site should idealy give the worst readings to be found in the pool, and should be chosen with this in mind. There is little point taking a sample close to the return inlets, especially if there is automatic chemical control.

The water sample should be taken from about 12" - 18" (30cm - 45cm) below the surface.

Use the sample immediately.


THE COMPARATOR

This is probably the most popular method for carrying out regular Proportional Colour water tests, and is much favoured by commercial pool operators, environmental health officers, and many swimming pool engineers. The Comparator enables the colour of the sample under test to be accurately compared with a series of colour standards mounted in a "wheel". The comparator has either two viewing ports, or one port viewing through a split prism - so that the color standard and the water sample appear to the eye to be next to each other - and so a more accurate assessment of the sample colour can be made.

The sample under test with the appropriate reagent applied - usually in a special 10ml cuvette (test tube) is placed in one compartment of the comparator. Another similar cuvette with just the pool water in it, is placed in the other compartment as a "blank" for corrections for cloudy or coloured water. The user looks through the viewing port(s) and can see on one side the coloured sample with reagent, and next to it the colour standard (viewed through the blank) on the "wheel" or disc. The wheel is then slowly rotated, bringing the different colour standards into view in turn. When the two colours match (the sample with the reagent and the colour standard), the level of the particulal chemical being tested will be found printed on the disc - lined up with a small viewing window.

The comparator is very easy to use, and with very little practice a new operator can be achieving very accurate results in seconds.

Comparators usually have a white translucent back to diffuse daylight and provide a white screen against which the sample and colour standards are viewed. Most makes of comparator have the facility to be connected to a "daylight box" which can be either battery or mains powered, and provides a constant, standard source of the correct light.


THE SHAKER TUBE

This is a simple tube or sample bottle and usually has a push-fit cap to seal it. Shaker tubes are usually either 50ml or 100ml capacity and are used for the "Titration" tests. As the name suggests, each time reagent is applied, the cap is replaced and the sample can be shaken to quickly mix and distribute the reagent in the sample under test. In practice, some tablet reagents don't dissolve easily and crushing and stirring has employed to thoroughly dissolve and mix each tablet.

An alternative method sometimes used is to crush a fixed number of tablets in a shaker tube with a few drops of water and form a slurry. The sample water is then slowly added until the colour change occurs. The volume of water in the tube indicates the level of the particular chemical being tested

Most Shaker Tubes have graduations marked on the side to enable different volumes of water to be tested as a sample, and also to allow easy dilutions of water samples for other tests, and plastic Shaker Tubes are ideal for collect the initial water samples.


THE TURBIDITY TEST TUBE

The Turbidity Test Tube usually comprises of two tubes, one inside the other. The outer tube has markings to enable the operator to easily add the the correct amount of sample water to test. The reagent is then added, which causes the sample to become cloudy. The degree of cloudiness or Turbidity is dependant on the level of the chemical being tested in the sample. The innner tube has graduations on the side, a black spot or similar on the inside bottom of the tube, and a small hole at the bottom of one side. This inner tube is slowly lowered into the cloudy sample in the outer tube. The sample water enters the inner tube through the small hole, and as the tube is lowered further into the sample, the inner tube steadily fills. The operator carefully looks down the centre tube at the black spot which, due to the cloudy sample slowly becomes more difficult to see. At the point where the black spot just disappears, the inner tube movement is stopped and a note taken of where the water sample surface is in relation to the inner tube. The graduations on the inner tube are numbered and this gives an indication of the level of the chemical being tested.

There are variations on this method where the simple is mixed with the reagent in one bottle and the cloudy solution slowly poured into a graduated cuvette with the black spot on the base. Again, the operator carefully monitors the visibility of the black spot and when it just disappears, the level of sample water in the cuvette is compared to the graduations on the side to determine the particular chemical level.


WATER TEST METHODS

The Methods detailed below are those used in the popular commercial comparator water test kits, which also utilise titration and turbidity tests. We seldom conduct a TDS test, since we consider this an outdated and inaccurate method of assesing water quality. For details and reasons please visit Page 8 - Basic Water chemistry (link there from the top or bottom of this page)

 


CHLORINE TESTS

FREE CHLORINE

  • Min - 1.5 ppm
  • Ideal - 1.5 - 3.0 ppm
  • Max - 5.0 ppm

Method - Proportional colour

Equipment Required - Comparator, Light Source, Chlorine Disc, 3 x 10 ml cuvettes, Stiring rod, DPD No 1 reagent

Fit the chlorine disc into the comparator.

Rinse out 3 cuvettes thoroughly with sample water and leave one filled to the 10ml mark and place it it in the left hand compartment of the comparator to act as a "blank" behind the colour standards.

Fill the second cuvette to the 10ml mark with sample water also.

Place a few drops of sample water from the second cuvette into the third cuvette, and add one DPD No 1 test tablet. Crush into a slurry and then make up into 10ml with the rest of the water from the second cuvette, and thoroughly mix.

Place this cuvette in the righthand compartment of the comparator and match against the colour disc immediately.

Read the value of Free Chlorine in ppm or mg/l from the bottom right hand window of the comparator.

NOTES

The Free Chlorine reading MUST be completed within about 15 - 20 seconds of adding the DPD No 1 tablet. If the sample is left for longer, the colour may deepen and intensify leading to a grossly inaccurate assesment of the free chlorine levels.

High levels of chlorine can bleach the indicator colour to imply a low or non existant free chlorine level. The correct level can be found by a suitable dilution ratio with distilled water.

 

TOTAL CHLORINE

  • The Total Chlorine level should not exceed 5 ppm.

Method - Proportional colour

Equipment Required - Comparator, Light Source, Chlorine Disc, 3 x 10 ml cuvettes, Stiring rod, DPD No 1 + DPD No 3 reagent

After completing the Free Chlorine test, add one DPD No 3 tablet to the cuvette containing the dissolved DPD No 1 tablet.

Crush the DPD No 3 tablet and mix thoroughly, then allow to stand for 2 minutes.

After 2 minutes has elapsed place the cuvette in the comparator as before and match against the same disk.

Read the Total Chlorine level in ppm or mg/l from the bottom right hand window of the comparator.

NOTE

High levels of chlorine can bleach the indicator colour to imply a low or non existant free chlorine level. The correct level can be found by a suitable dilution ratio with distilled water.

 

COMBINED CHLORINE

  • Max - 0.5 ppm
  • Absolute Max - 1.0 ppm
  • The Free Chlorine level should always be more than 3 times the Combined Chlorine level

To determine the level of combined chlorine present, subtract the reading for Free Chlorine from the reading for Total Chlorine.

The result is the Combined Chlorine level in ppm or mg/l


pH TESTS

  • Min - 7.2 pH
  • Ideal - 7.4 pH (usually)
  • Max - 7.6 pH

Method - Proportional colour

Equipment Required - Comparator, Light source, pH Disc, 2 x 10 ml cuvettes, Stiring rod, Phenol Red reagent

Fit the pH disc into the comparator.

Rinse out 2 cuvettes thoroughly with sample water and leave one filled to the 10ml mark and place it it in the left hand compartment of the comparator to act as a "blank" behind the colour standards.

Fill the second cuvette to the 10ml mark with sample water and add one Phenol Red test tablet.

Crush the tablet and mix thoroughly.

Place this cuvette in the righthand compartment of the comparator and match against the colour disc.

Read the pH Value from the bottom right hand window of the comparator.

NOTE

High levels of chlorine or bromine can cause an incorrect indicator colour, or even bleaching of the indicator colour, Do NOT attempt to test a diluted sample for pH. Accurate pH test results can only be achieved when the chlorine level is within normal safe pool limits.


TOTAL ALKALINITY TEST

  • Min - about 60 ppm
  • Ideal - 90 ppm - 120 ppm
  • Max - about 160 ppm

Method - Colour titration

Equipment Required - 50 ml or 100 ml Shaker Tube, Total Alkalinity test reagent

Fill the shaker tube to the 50 ml mark with sample water.

Add 1 Total Alkalinity Test tablet and shake tube to disintigrate and thoroughly mix the tablet. The sample water should become straw yellow in colour.

Keeping a note of the number of tablets used, continue to add and mix tablets one at a time until the sample changes from yellow to a bright pink.

Calculate the Total Alkalinity in ppm/mg/l from the formula :- (Number of tablets x 40) - 20

Example: sample takes 3 tablets to titrate (change colour). 3 x 40 = 120. 120 - 20 = 100. The T.A. is 100 ppm (or mg/l)

NOTE 1: Systems using chlorine gas for disinfection should ensure that their T.A. is at the maxim, to buffer the highly corrosive chlorine gas

NOTE 2: Greater accuracy can be achieved by using a 100 ml sample and the formula (Number of tablets x 20) - 10

NOTE 3: High levels of chlorine or bromine can bleach the indicator colour, making the colour change difficult to detect. Do NOT attempt to test a diluted sample for Total Alkalinity, but wait for the chlorine or bromine to be reduced.

NOTE 4: The presence of Cyanuric Acid (chlorine stabilizer) can interfere with the T.A. test an cause a higher level of T.A. to be indicated. If the cyanuric acid level in the sample is greater than 50 ppm, deduct 1/3rd of the cyanuric acid level from the apparent T.A. level to find the Corrected Total Alkalinity level.

Example: T.A. test indicates 160 ppm and the cyanuric acid level indicates 120 ppm

1/3rd of 120 (cyanurate) = 40. and then 160 (T.A.) - 40 = 120. Therefore the Corrected T.A. is 120 ppm (or mg/l)


CALCIUM HARDNESS TEST

  • Min - about 250 ppm
  • Ideal - about 300 ppm
  • Max - around 600 ppm

Method - Colour titration

Equipment Required - 50 ml or 100 ml Shaker Tube, Calcium Hardness test reagent

Fill the shaker tube to the 50 ml mark with sample water.

Add 1 Calcium Hardness Test tablet and shake tube to disintigrate and thoroughly mix the tablet. The sample water should become pink in colour.

Keeping a note of the number of tablets used, continue to add and mix tablets one at a time until the sample changes from pink to violet.

Calculate the Calcium Hardness in ppm/mg/l from the formula :- (Number of tablets x 40) - 20

Example: sample takes 8 tablets to titrate (change colour). 8 x 40 = 320. and 320 - 20 = 300. so the Calcium Hardness is 300 ppm (or mg/l)

NOTE 1: Greater accuracy can be achieved by using a 100 ml sample and the formula (Number of tablets x 20) - 10

NOTE 2: High levels of chlorine or bromine can bleach the indicator colour, making the colour change difficult to detect.


CYANURIC ACID TEST

  • Min - 0 ppm (indoor pools)
  • Min - 20 ppm (outdoor pools only)
  • Ideal - 0 ppm (indoor pools)
  • Ideal - 30 ppm (outdoor pools only)
  • Max - 50 ppm (operational, to avoid chlorine 'lock')
  • Max - 200 ppm Maximum safe level for health

(Note: - There is still a lot of confusion and 'misinformation' about Cyanuric Acid. The maximum SAFE level and the maximum OPERATIONAL level are two entirely different standards. Research has shown that with levels above 50 ppm the tendancy for chlorine to 'lock' progressively increases. Although swimming pools are often found to be crystal clear despite having excessively high CYA levels, a maximum of 200 ppm has been determined for health reasons. Chlorine 'Lock' occurs at an indeterminate level of CYA and is dependant of the overall water chemistry. We have documented evidence of one pool being 'locked' at 70 ppm CYA, whilst another still crystal clear at 200 ppm CYA. High levels (over 50 ppm) of CYA also attack copper, stainless steel and other metals, and therefore the Cyanuric level should always be maintained below 50 ppm.)

Method - Proportional Turbidity

Equipment Required - Turbidity Test-Tube kit, crusher/stirrer, Cyanuric acid turbidity test reagent

Separate the Double Tube Turbidity Tester assembly, and fill the outer tube to the top line with sample water.

Add 1 Cyanuric Acid test tablet, crush and mix thoroughly.

When thoroughly mixed, a cloudy solution indicates the presence of Cyanuric Acid.

Slowly insert the square graduated inner tube into the round outer tube ensuring the friction cap is in position, so that the inner tube slowly fills with the cloudy sample water.

Viewing from above, adjust the inner tube up and down until the black spoy on the base of the tube is "just" not visible.

Read the cyanuric acid level in ppm or mg/l from the graduations level with the surface of the solution in the inner tube.

NOTE: If the solution is too cloudy to obtain an accurate reading, then dilute the sample by filling the outer tube to the bottom line with fresh sample water and making up to the top line with distilled water.

Carry out the test as before and multiply the result by 2.

If the solution is still too cloudy further dilution should be effected until an accurate reading is obtained


SULPHATES TEST

  • Max - about 300 ppm

Method - Proportional Turbidity

Equipment Required - Turbidity Test-Tube kit, crusher/stirrer, Sulphates turbidity test reagent

Separate the Double Tube Turbidity Tester assembly, and fill the outer tube to the top line with sample water.

Add 1 Sulphates Turbidity test tablet, crush and mix thoroughly.

When thoroughly mixed, a cloudy solution indicates the presence of Sulphates.

Slowly insert the square graduated inner tube into the round outer tube ensuring the friction cap is in position, so that the inner tube slowly fills with the cloudy sample water.

Viewing from above, adjust the inner tube up and down until the black spoy on the base of the tube is "just" not visible.

Read the number from the graduations level with the surface of the solution in the inner tube and multiply this number by 2 to determine the Sulphates level in ppm or mg/l

NOTE: If the solution is too cloudy to obtain an accurate reading, then dilute the sample by filling the outer tube to the bottom line with fresh sample water and making up to the top line with distilled water.

Carry out the test as before and multiply the result by 4.

If the solution is still too cloudy further dilution should be effected until an accurate reading is obtained


CHLORIDES TEST

  • Max - about 600 ppm

Method - Colour titration

Equipment Required - 10 ml cuvette or 100 ml shaker tube, crusher/stirrer, Chlorides test reagent

Fill a 10 ml cuvette to the mark with sample water.

Add 1 Chlorides test tablet and crush and stir to disintegrate and mix the tablet. The sample should become bright yellow.

Keeping a note of the number of tablets used, continue to add and mix tablets one at a time until the sample changes from yellow to brown.

Calculate the Chlorides level in ppm/mg/l from the formula :- (Number of tablets x 100) - 100

Example: sample takes 4 tablets to titrate (change colour). 4 x 100 = 400. and 400 - 100 = 300. so the Chlorides level is 300 ppm (or mg/l)

NOTE 1: For low levels a greater accuracy can be achieved by using a 100 ml sample and the formula (Number of tablets x 10) - 10

NOTE 2: High levels of chlorine or bromine can bleach the indicator colour, making the colour change difficult to detect.


WATER BALANCE

There is a relationship between the pH Value, the Total Alkalinity, the Calcium Hardness, and the Temperature of pool water.

These values, in combination, determine whether the water is Corrosive, Neutral, or Scale Forming.

There are two principle methods of determining the Water Balance - the Langelier method and the Palintest method. Both of these methods will allow you to assess your Water Balance.

We consider the Palintest method to be the easiest. We have also re-plotted the original figures and taken into account the warmer waters of present day swimming pools. The Water Balance tables we now use are very close to the original Palintest tables.

To calculate the Water Balance the figure for the pH Value is added to factors for Total Alkalinity, Calcium Hardness, and Temperature. The total figure - the Water Balance Index, is then compared with a range of index figures to determine the actual Water Balance description.

FACTOR TABLES

Total Alkalinity                         Total Alkalinity
Calcium Hardness                    Calcium Hardness
     PPM                FACTOR             PPM                FACTOR
      20 . . . . . . . . 0.90              320 . . . . . . . . 2.12
      40 . . . . . . . . 1.18              340 . . . . . . . . 2.15
      60 . . . . . . . . 1.40              360 . . . . . . . . 2.18
      80 . . . . . . . . 1.50              380 . . . . . . . . 2.22
     100 . . . . . . . . 1.60              400 . . . . . . . . 2.25
     120 . . . . . . . . 1.68              420 . . . . . . . . 2.30
     140 . . . . . . . . 1.75              440 . . . . . . . . 2.34
     160 . . . . . . . . 1.82              460 . . . . . . . . 2.40
     180 . . . . . . . . 1.88              480 . . . . . . . . 2.47
     200 . . . . . . . . 1.92              500 . . . . . . . . 2.50
     220 . . . . . . . . 1.96              520 . . . . . . . . 2.55
     240 . . . . . . . . 2.00              540 . . . . . . . . 2.60
     260 . . . . . . . . 2.05              560 . . . . . . . . 2.65
     280 . . . . . . . . 2.08              580 . . . . . . . . 2.70
     300 . . . . . . . . 2.10              600 . . . . . . . . 2.75
  • Water Temperature Below 70 deg F. SUBTRACT - 0.10
  • Water Temperature Above 80 deg F . . . ADD - 0.10
  • Water Temperature Above 90 deg F . . . ADD - 0.20

The BALANCE INDEX = pH value + T.A. Factor + C.H. Factor + Temperature Factor.

 

Index Figure Interpretation

BALANCE INDEX     WATER CONDITION
    Below 9.6  -  Highly Corrosive
  9.6 to 10.5  -  Corrosive
 10.6 to 10.9  -  Acceptable Balance
 11.0 to 11.2  -  Ideal Balance
 11.3 to 11.6  -  Acceptable Balance
 11.7 to 12.6  -  Scale Forming
   Above 12.6  -  Highly Scale Forming
EXAMPLE No 1:-

pH value 7.4

Total Alkalinity 100 ppm - ( factor = 1.60 )

Calcium Hardness 280 ppm - ( factor = 2.08 )

Temperature 84 Deg F. - ( factor = + 0.10 )

7.40 + 1.60 + 2.08 + 0.10 = a Water Balance Index of 11.18 = Ideal Balance
EXAMPLE No 2:-

pH value 7.7

Total Alkalinity 160 ppm - ( factor = 1.82 )

Calcium Hardness 360 ppm - ( factor = 2.18 )

Temperature 94 Deg F. - ( factor = + 0.20 )

7.70 + 1.82 + 2.18 + 0.20 = a Water Balance Index of 11.90 = SCALE Forming

 

If the pool water is classed as Scale Forming, scale will start to form - particularly in the heater or heat exchanger. Another favourite place for scale to form is in the Sand Filter, and this frequently causes the sand to solidify into a solid mass. Scale will also build up in the pool shell, covering tiles, ladders, and almost all other fittings. A Liner Pool will often have rough particles of scale adhereing to the vinyl liner, giving it a rough feel.

If the pool water is classed as corrosive, grout, cement, and plaster will be gradually destroyed, tiles will become loose, and the plaster or Marble finish will becoem very rough and pitted. Any metalic equipment will also suffer from corrosion particularly the copper heat exchangers found in most pool Gas Heaters, and cast iron circulation pumps and iron pipes.

Corrosive pool water which also suffers from a high Sulphates level will lose grout and possibly tiles very quickly. If the Chlorides level is very high the copper heat exchangers will not last very long.

The water balance should be regularly checked and adjusted for Ideal Balance. It is also important that the individual components are not permitted to stray outside their permitted parameters.


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