Pool Tests for Chlorine & pH

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General Points on Pool Water Testing

  • the equipment used should be clean and dry
  • reagent tablets should not be touched as this would affect the reading
  • COSHH assessments should be carried out on all reagent chemicals
  • all samples should be taken from the same, pre-determined point every time
  • staff should be trained in pool water testing
  • pool testing and effective lifeguarding cannot be carried out at the same time
  • photometers should be re-calibrated on an annual basis
  • if results are not as expected, always do an immediate re-test
  • put test tubes on a stable, flat surface when crushing the reagent tablets

 

Comparators

These are simple devices that work by inserting a sample of pool water next to another sample of pool water with a reagent dissolved in it into the comparator, and then inserting a colour wheel in front of the samples. The tester then holds the comparator up to the light and compares the colour of the two samples. The colour wheel is rotated until the closest match is found and a reading is then taken from the small circular display aperture. See an example of a comparator below.

 

 

 

A pool water testing comparator.

 

Photometers

These are devices that work electronically. A test tube containing a sample of pool water is placed in the device, which shines light through the sample. A reading is taken and the result is displayed on the device’s screen.
Palintest tests are based on measuring the intensity of colours produced by Palintest reagents and using Palintest photometers to measure that intensity of colour. This is colorimetry and can be defined as any technique used to evaluate an unknown colour in reference to known colours.
To avoid subjective measurement between test samples and colour standards, a colorimeter can be used for quantitative measurement of the amount of coloured light absorbed by a sample (with reagents added) in reference to an untreated sample (blank). See an example of a photometer below.

 

A pool water testing photometer.

 

Reagents

Pool water testing works by adding reagents to a sample of pool water and interpreting the results according to the colour of the sample once the reagent has had time to react with it. Different tests require different types of reagents. The type of testing equipment (comparator or photometer) will also influence the type of reagent that needs to be used.

 

Documentation

All tests carried out on the pool water should be recorded accurately and stored in a system that allows for easy retrieval. Electronic recording and storage of data is acceptable, but may not be the most practical option, given the environmental conditions.

Click play to watch a video demonstration

 

Free Chlorine Test

  1. Rinse out two test tubes with pool water.
  2. Fill one up to the 10ml mark, leave the other empty but damp.
  3. Put a DPD 1 tablet into the empty tube, without touching the tablet.
  4. Watch the reaction of the tablet. If you can see any pink colour – there is chlorine.
  5. Fill the test tube with the DPD 1 tablet to the 10ml mark.
  6. Crush the tablet with the crushing rod. Ensure the tablet is completely dissolved and there are no bubbles left in the test tube before continuing.
  7. If the water is no longer pink – you have too much chlorine and it has bleached the colour out of the sample. Do a retest to confirm.
  8. Obtain a reading according to the type of tester you are using (comparator or photometer). See below:

 

For Comparator For Photometer
  1. Put ‘blank’ test tube in the left slot and the test tube with the DPD 1 tablet into the right slot.
  2. Insert the chlorine wheel into the comparator so that you can see the numbers displayed in the little circular aperture.
  3. Hold the comparator up to a good source of light and observe the colour match.
  4. Rotate the chlorine wheel until the best match is achieved.
  5. Record the reading on the pool test sheet.
    1. Put the ‘blank’ test tube into the slot on the photometer.
    2. Put the light cap (if there is one) over the test tube*.
    3. Turn the photometer on and select the free chlorine mode.
    4. You will be prompted to ‘zero’ the photometer.
    5. Swap the blank with the test tube with the DPD 1 tablet.
    6. Remember to replace the light cap.
    7. You will be prompted to press the test button.
    8. Record the reading on the pool test sheet.

 

 

* Photometers work by shining a light through the sample. All external light needs to be prevented from ‘leaking’ into the sample. To achieve this, some photometers have a separate light cap. Other photometers achieve it by the test tube caps being designed to fit snugly so that it stops light entering the sample.

 

Total Chlorine Test

  1. Add a DPD 3 tablet to the test tube that already contains the DPD 1 tablet.
  2. Crush the tablet with the crushing rod.
  3. Wait for 2 minutes
  4. Take the reading in the same way as for the DPD 1 test.
  5. Record the reading on the pool test sheet.

 

 

Depending on the model of photometer you are using, you may have to press the ‘mode’ button in order to ensure that the device is set up for reading total chlorine (rather than free chlorine). Also, some photometers have a built in timer that counts the two minutes down automatically.

 

Calculating the Combined Chlorine Reading

The combined chlorine is worked out by simply taking the free chlorine result away from the total chlorine result:

 

Total Chlorine – Free Chlorine = Combined Chlorine

 

pH Test

  1. Rinse out another test tube with pool water (use the same ‘blank’ that was used with the chlorine tests).
  2. Fill the test tube up to the 10ml mark.
  3. Put a Phenol Red tablet into the sample, without touching the tablet.
  4. Crush the tablet with the crushing rod. Ensure the tablet is completely dissolved and there are no bubbles left in the test tube before continuing.
  5. Obtain a reading according to the type of tester you are using (comparator or photometer). See below:

 

For Comparator For Photometer
  1. Put ‘blank’ test tube in the left slot and the test tube with the Phenol Red tablet into the right slot.
  2. Insert the pH wheel into the comparator so that you can see the numbers displayed in the little circular aperture.
  3. Hold the comparator up to a good source of light and observe the colour match.
  4. Rotate the chlorine wheel until the best match is achieved.
  5. Record the reading on the pool test sheet.
  1. Put the ‘blank’ test tube into the slot on the photometer.
  2. Put the light cap (if there is one) over the test tube*.
  3. Turn the photometer on and select the pH mode.
  4. You will be prompted to ‘zero’ the photometer.
  5. Swap the blank with the test tube with the Phenol Red tablet.
  6. Remember to replace the light cap.
  7. You will be prompted to press the test button.
  8. Record the reading on the pool test sheet.

 

 

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