Testing for Water Balance

• pH

  Carry out the usual test for pH - e.g. fill a 10ml test phial with pool water, drop a phenol red tablet into the sample and match the colour on your colour comparator.

• Total alkalinity

  Take a 100ml pool water sample in a stoppered bottle. Using Palintest Alkalinity M tablets, add one tablet at a time shaking the bottle until dissolved. Keep adding tablets until the colour changes from yellow to bright pink. Count the number of tablets used and work out the alkalinity - Alkalinity = (number of tablets x 40) - 20 ppm

• Calcium hardness

  Take a 100ml pool water sample in a stoppered bottle. Using Palintest Calcium Hardness tablets, add one tablet at a time shaking the bottle until dissolved. Keep adding tablets until the colour changes from pink to bright violet. Count the number of tablets used and work out the hardness - Hardness = (number of tablets x 20) - 10 ppm

• Total dissolved solids (TDS)

  Total dissolved solids are measured using a conductivity meter. This equipment is quite expensive and is not normally at the disposal of the private pool owner, so you have 2 choices:

  1. Take your sample of pool water to your pool centre and ask them to measure TDS for you. They will normally be happy to do this for you free of charge if you usually buy your chemicals etc from them.

  2. As TDS plays a less important part in the calculation than the other factors you can estimate it, but do bear in mind that this will then only give you a rough idea of whether the water is scale forming or corrosive. As a guide, for pools which have been recently refilled, use a figure of 750ppm. For pools which have not been recently refilled, or where there has been little water replacement by backwashing, or where cyanuric acid levels are above 200ppm, use a figure of 1500ppm for TDS.

• Water temperature

  Finally take the temperature of the pool water in degrees Farenheit.

You now have all the information you need to determine the water balance. Procede to the next section.

3. Filling in the interactive form.

Using your readings for pH, total alkalinity, calcium hardness, total dissolved solids and temperature (in degrees F), fill in the form below and scroll down for results.

4. Interpreting the results and taking remedial action.

Do bear in mind that if you have had to estimate a figure for total dissolved solids, the results will not be accurate, but will only give you a rough idea as to water balance

What to do:

1. If the water is slightly scale forming
   
2. If the water is corrosive
   
3. If the water is scale forming - above +0.3

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1. If the result shows the water is slightly scale forming (i.e. between 0 and 0.3), that is what you are aiming for. The pool is protected and you need take no further action.

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2. If the result of the calculation is negative, you will have noticed in the table that there is a warning that the water is corrosive . Look carefully at your readings for pH, total alkalinity and calcium hardness.
   • pH carries more weight in the calculation than all the other factors. It should be between 7.2 and 7.6. If pH is towards the bottom end of the scale, you may be able to correct the water balance by doing no more than raising pH alone . Add soda ash daily at a rate of 1kg for every 22,000 gallons until it approaches the mid point of the pH band.

   • Total alkalinity should be between 100ppm and 200ppm. If your reading is toward the bottom end of the scale, raise the TA to the mid point of the band by adding bicarbonate at a rate of 3kg per 22,000 gallons.

   • Calcium hardness should be between 100ppm and 500ppm. If your reading is toward the bottom end of the scale, raise the CH to the mid point of the band by adding calcium chloride at a rate of 2kg per 22,000 gallons.

   These measures should produce satisfactory water balance - if in doubt, re-test. Note: You should attempt to ensure all parameters fall within recommended bands. A high total alkalinity is not a satisfactory way of compensating for a low calcium hardness.

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3. If the result of the calculation is higher than 0.3, you will have noticed in the table that there is a warning that the water is scale forming. Look carefully at your readings for pH, total alkalinity and calcium hardness.
   • pH carries more weight in the calculation than all the other factors. It should be between 7.2 and 7.6. If pH is towards the top end of the scale, you may be able to correct the water balance by doing no more than lowering pH alone. Add dry acid daily at a rate of 1kg for every 22,000 gallons until it approaches the mid point of the pH band.

   • Total alkalinity should be between 100ppm and 200ppm. If your reading is toward the top end of the scale, lower the TA to the mid point of the band by adding dry acid to one spot in the pool at a rate of 2kg per 22,000 gallons. Correct pH first if this needs to be done.

   • Calcium hardness should be between 100ppm and 500ppm. If your reading is toward the top end of the scale, lower the CH to the mid point of the band by replacing some of the pool water with fresh.

   These measures should produce satisfactory water balance - if in doubt, re-test.