• Alkalinity
  • Desinfection
  • pH-value
  • Water balance
  • Winter preparation


The total alkalinity (TA) is the total amount of alkaline material, like bicarbonates and hydroxides. The term TA is often confused with pH. The TA works as buffer against sudden changes in the pH value. The lower the TA value, the easier the pH can be adapted by adding small amounts of acid or base. The higher the TA value, the harder it gets to change the pH value. The buffer capacity of the water is mainly determined by the concentration of carbonate, bicarbonate and carbon acid.

Cyanuric acid

Influence of cyanuric acid on measuring of TA 

If there is cyanuric acid in the water, it will influence the reading of the TA. The reading will give a too high result in this case. Depending on the pH-value, the value measured should be corrected with a percentage of the table below:
Usually a correction factor of about 30% will do, except in those cases in which the pH is too low and / or the value of cyanuric acid is very high.
With a value of cyanuric acid <= 50 ppm and a measured TA is >= 100 ppm a correction is not necessary.

pH 7.2 7.5 7.8
correction percentage 25 % 30 % 35 %

Ideal value

The ideal TA value lies between 100 and 150 ppm. With a higher value than 175 ppm a lot of acid or base is necessary to change the pH value. Below 60 ppm the pH value is not stable.It may take a while before you reach the favourable TA-value, because the pH-value should never drop below 6.8 or rise above 8.

You can adapt the pH-value and the TA-value by adding small amounts of the right products. Also check the instructions on the label.Once the TA-value is correct, regular tests are usually no longer needed.

Once the TA value is correct it is generally no longer necessary to regularly measure the TA value.

Problems with too low TA value Problems with too high TA value
PH value fluctuates too much PH value hard to correct, pH value hardly changes
Tendency to corrosion Cloudy water
  Non-efficient chlorine usage
  Big volume of melpool pH necessary for pH correction


Disinfection of pool water is absolutely necessary. Someone who goes swimming without showering can bring up to 10 billion micro-organisms into the water, even a showered swimmer can carry up to 100 million micro-organisms with him. From research done in France it appeared that 1 swimmer ads an average of 30 million micro-organisms and 0.5 grams of organic material to the water.

In order to control and prevent unwanted and dangerous bacteria, swimming pool water needs to be disinfected. Of course, this should be done continuously.

Environmental effects

The use of chlorine in swimming pools hardly affects the environment. A pool is a closed system and so the pool water does not get into contact with the environment. When draining pool water with a very high chlorine value or with an extremely low pH-value one could speak of a negative effect. Poolwater does not differ much from water produced by a drinking water company.


The pH-value of pool water is a very important factor. There is no fixed ideal pH-value for pool water. A wrong pH-value can cause many problems. The pH-value, which should usually be maintained, can be exactly calculated by means of Langelier index. As a guide we indicate on our labels a desired pH-value of 7.2 – 7.4. This value works in practice.

The pH of the water can change by::

  • Rain water
  • Adding certain chemicals and by reaction with other chemicals
  • Adding tap water
  • Dust and organic material which lands in the water by wind and / or swimmers


PH-corrections should be done in small steps. Increase or decrease the pH-value in steps of 0.4 maximum per time. Turn on the pump! Afterwards wait for 8 hours (24 hours preferably) before taking a next step.


A maladjusted pH-value can cause many problems:

Problems with a too low pH-value (Corrosive water) Problems with a too high pH-value (Alkalinity)
stains blocked filter
metals dissolve less water circulation
problems to maintain water balance cloudy water
eye- and skin irritation problems to maintain water balance
formation of chloramines eye- and skin irritation
high chlorine use  

The pH-value of pool water needs to be checked regularly. The pH-value can be corrected by using Melpool pH- or Melpool pH+.

The total alkalinity (TA) also has influence on the pH-value. The TA should at least be 60 ppm. At too low a TA-value the pH-value of the water is unstable. You can increase the TA-value by using Melpool TA+.

Water balance 

Water balance 

One can speak of a good water balance when the water is neither corrosive nor alkaline. The concept of the water balance is based on the fact that, by nature, water needs specific minerals. These minerals can be considered as food for the water. With not enough food the water gets hungry or "corrosive", with too much food the water gets overfed (saturated) and it gets alkaline.


Which parameters are needed to calculate the water balance? 

The temperature of the water in degrees Celsius

Of course, the temperature of the water is measured with a thermometer. The other parameters are determined with testkits available at professional pool shops.

The pH-value of the water

The total alkalinity of the water

Attention! If you use stabilised products (melpool 63/G, melpool 90/200 of melpool 90/20) the measured value of total alkalinity needs to be corrected. To be able to do this you also have to measure the concentration of cyanuric acid.

For the correction you need to determine the following parameters:

TA1 = the measured total alkalinity in ppm

CA = the measured value of cyanuric acid in ppm

PHf = the pH-factor, this is the number which is mentioned in the table below in column pHf. If your measured pH-value is 7.2 you use the pHf-value of 0.26.

To do the correction you use the following formula:

TA = TA1-(pHf x CA).

The TA value calculated this way needs to be used to calculate the water balance.

Calculation example

Originally you measured a TA-value of 185 ppm. The cyanuric acid value of the pool is 70 ppm and the measured pH-value is 7.4.

TA = 185 – (0.3 x 70) = 164

The calcium hardness of the water

The total quantity dissolved substances

The total amount of dissolved solids has a restricted influence on the calculation of the water balance. If you are not able to calculate the total dissolved solids, you can use 1000 as your value. If your water was refreshed over a year ago you can use 2000 as your value.

Factors that determine the water balance 

  • pHF – pH (acid value) factor
  • CF – calcium hardness factor
  • AF – total alkalinity factor
  • TF – total dissolved solids factorThe Saturation Index (S.I.) is calculated with above-mentioned parameters.

SI = pH + TF + CF + AF - TDSF:

temp oC TF CH ppm CF TA ppm AF TOVS ppm TOVSF pH pHF
0 0,0 5 0,3 5 0,7 0 12,0 6,5 0,11
3 0,1 25 1,0 25 1,4     7,0 0.22
8 0,2 50 1,3 50 1,7 1000 12,1 7,2 0.26
12 0,3 75 1,5 75 1,9     7,4 0.3
16 0.4 100 1,6 100 2,0 2000 12,2 7,6 0.33
19 0,5 150 1,8 125 2,1     7,8 0.35
24 0,6 200 1,9 150 2,2 3000 12,5 8,0 0.36
29 0,7 250 2,0 200 2,3     8,5 0.38
34 0,8 300 2,1 300 2,5 4000 12,3    
41 0,9 400 2,2 400 2,6        
53 1,0 600 2,35 800 2,9 5000 12,35    
    800 2,5            

After the values of pH, temperature, alkalinity and TDS are measured, the calculation of the S.I. can be done. The accessory factors used in the formula above can be found in the table above. With a temperature of 19 degrees the temperature factor is TF 0.5 and with a pH-value of 7.6 the pHF is 0.33, etc.

Calculation example:

Swimming pool parameters   Corresponding table values
Temperature 24°C TF = 0.6
pH 7.2  
CH (calcium hardness) 200 ppm CF = 1.9
TA (total alkalinity) 100 ppm AF = 2.0
TOVS (total dissolved solid substances) 1000 ppm TOVSF = 12.1

SI = pH + TF + CF + AF - TOVSF
SI = 7.2 + 0.6 + 1.9 + 2.0 - 12.1 = - 0.4  (acceptable balance, tendency to corrosion).

Reading out the water balance

After making the calculation of the S.I. the situation of the water balance can be determined in the table below.

SI (Saturation Index) Condition of the water Required treatment
< -0,5 Tendency to corrosion See problems/solutions
- 0,5 tot - 0,2 Acceptable balance Test water regularly
- 0,1 tot 0,1 Ideal water balance None
0,2 tot 0,5 Acceptable balance Test water regularly
> 0,5 Tendency to alkalinity See problems/solutions

Winter preparation

  • Test the water and bring it back into balance, if necessary. If you do not bring the water into balance, you will probably get stains, scaling and damaged equipment.
  • Clean the pool. Use Melpool GEL to cleanse the water line. Brush the sides of the pool, if necessary.
  • Clean the skimmer baskets and also cleanse the front filter of the pump. Then vacuum.
  • Backwash filter and clean with Melpool DET.
  • Dose Melpool CAL according to instructions.
  • Give the pool a shock treatment, then let the pump run for at least 24 hours.
  • Dose Melpool QAC (prevents algae growth) according to instructions.
  • Partly let out the water until right below the injectors.
  • Drain the equipment. Turn off the pump. Plastic items like skimmer baskets, prefilters, vacuum hoses and thermometers last longer if stored frost-proof.
  • Cover the pool, so no pollution can enter.
  • Store pool chemicals in a cold and dry place.