Understanding water balance

The importance of good water balance in a pool

The water in a pool must have good balance to ensure bathing is pleasant and safe, and to maintain the longevity of pool equipment.

The water balance is based on 3 parameters:

• pH (Potential of Hydrogen)
• TA (Total Alkalinity)
• TH (Hydrotimetric Titer) which gives information about the water hardness.

A well-regulated pH prevents irritation to the skin and eyes of bathers whilst protecting the installations against corrosion or scaling. A correct TH avoids limescale deposits or water that is too soft, and the TA plays an important role in pH stabilisation.

The values of these parameters must be controlled, corrected and maintained to achieve crystal clear pool water and good disinfection. It is recommended that these values are checked regularly during the season. Imbalance of the water can cause algae to proliferate, making the water green and slimy, and increasing the risk of diseases. The algae can also obstruct filtration systems and make pool maintenance much more complex and costly.

Discover how to adjust these parameters to maintain a pool in perfect condition throughout the year!

The pH: provides information about the degree of acidity or alkalinity of the water

The Potential of Hydrogen indicates the acidity or alkalinity of the water. It must be monitored to ensure effective disinfection but also to reduce corrosion, limescale deposits and to maintain comfortable swimming conditions.

Ideally, it should be between 7 and 7.4.

The pH can fluctuate due to various factors:

• Decrease: heavy use of the pool, or due to rain water
• Increase: an increase of the water temperature or the addition of certain disinfectants such as calcium or sodium hypochlorite.

A pH of less than 7 means that the water is aggressive. This leads to corrosion of the metal parts, deterioration of tiling grout, and a risk of irritation of the eyes and mucous membranes.

A pH higher than 7.4, on the other hand, means that the water will cause scaling. This results in limescale deposits, scaling up of the pipes, filter media and salt chlorination plates, which reduces the effectiveness of chlorine and makes the water cloudy. 

How is the pH measured?

Several methods can be used to measure the pH level of your water:

• Phenolphthalein indicator solution: this liquid turns a certain shade of red for each pH value. However, this method is not very precise and the liquid will only last for 2 months. 
• Strips: they allow manual control and are more precise and less fragile.
• Red Phenol tablets: used for manual control or with a photometer.

How can pH be corrected?

It is possibile to decrease or increase the pH using different products. We advise you to refer to the recommended quantities on the product information sheets.

To reduce the pH:

• In the case of automatic regulation by dosing pump: liquid pH reducer (sulphuric acid 15%).
• In the case of manual correction: with powder pH reducer (sodium bisulphate).

To increase the pH:

• In the case of automatic regulation by dosing pump: add liquid pH increaser (sodium hydroxide in solution or caustic soda).
• In the case of manual correction: add powder pH increaser (sodium carbonate). Note that this also increases the TA.

Caution! Hydrochloric acid must not be used with a salt chlorinator. Aside from the toxic vapours it releases, it contains chlorides, which, added to those produced by the salt chlorination, make the water very corrosive.

The TH: indicates the water hardness

The TH (Hydrotimetric Titer) indicates the water hardness, in other words the concentration of Calcium Ca²+ and Magnesium Mg²+ ions present in the water.

The parameter is usually expressed in °f (French degrees). 1°f = 10 ppm, so 10 mg/l.

A TH below 10 °f indicates “soft” water which is aggressive and corrosive.

A TH higher than 12 °f indicates “hard” water which causes scaling.

With a salt chlorinator, the ideal TH valye is approximately 15 °f. However, it must not exceed 25 to 30 °f.

How is the TH measured?

You can measure the TH using tablets, strips or a photometer.

How is the TH corrected?

To decrease the TH you can use a TH reducer or an anti-limescale product. We advise you to use the doses recommended in the information sheet for your product.

The TA: the buffering capacity of the water

The Total Alkalinity (TA) is the capacity of the water to maintain a stable pH when acid or alkali is added. It is expressed as the quantity of carbonates CO3²- and bicarbonates HC03- present in the water.

The TA value influences the pH value and its stability. A TA that is too high will make correction of the pH difficult and leads to scaling risks. Inversely, a TA that is too low allows the pH to be corrected easily but makes stabilisation of the value more difficult.

The TA is expressed in °f (French degrees). 1 °f = 10 ppm, so 10mg/l.

Ideally, the TA is between 8 and 20 °f.

How is the TA measured?

You can measure the TA using tablets, strips or a photometer.

How is the TA corrected?

The TA can be decreased or increased using different products. We advise you to refer to the recommended quantities on the information sheets of your products.

To reduce the TA:

• In the case of manual regulation, add powder pH reducer (sodium bisulphate)
• In the case of automatic regulation with a dosing pump, add liquid pH reducer (sulphuric acid 15%).

To increase the TA:

• In the case of manual correction, add powder pH increaser (sodium carbonate).

To summarise:

The Taylor balance can also be used to determine the ideal pH and TA values.