Water balance is defined as a condition where the water is neither corrosive nor scale forming. The major factors in determining water balance are pH, total alkalinity and calcium hardness. The water supply also plays a significant role in water balance and this is discussed in the hard and soft water areas section.

pH
Maintaining the correct pH level in your pool plays an important role in how effective the chlorine is. The pH scale runs from 0 - 14 with 7 being neutral. Anything above 7 is considered alkaline and anything less than 7 is considered acidic. In the context of pool water 7.2 - 7.6 is the required range. Anything above 7.6 (more alkaline) reduces the effectiveness of the chlorine and can therefore promote viruses and bacteria. Anything below 7.2 (more acidic) makes the water corrosive and uncomfortable to swim in, causing irritation to the bather's eyes and skin.

Altering the pH level on your pool is a difficult procedure due to the effect the alkalinity level has on it. The ideal range for the alkalinity level is 80 - 160 ppm. If this is not sustained it will ultimately affect the pH level. If the alkalinity level is too low then this will create 'pH bounce' meaning the pH level will fluctuate. If the alkalinity level is too high then this will create 'pH lock' meaning any alterations will not affect the pH level and the results will become inaccurate. Therefore it is important to make sure the alkalinity level is correct before any pH alterations are carried out. After the correct alkalinity level is established test the pH level of the water. If the pH level needs increasing further, add sodium carbonate (pH plus) and if it needs decreasing add sodium bisulphate (pH minus).

Stating an accurate dosing amount can often be difficult due to the different natures of water supplies around the UK. The correct level required for your pool will become evident after a few doses, but as a general guide dissolve 500 grams for every 10,000 gallons in a bucket of warm water and distribute around the pool. Leave the filter pump running for 24 hours and then re-test.

Alkalinity
As mentioned earlier the alkalinity level influences the pH level of water. Therefore it is vital that the alkalinity level is kept within the range of 80-160ppm to help keep the pH of the water correct. If the alkalinity level is too high then this can lead to scale forming on the fixtures and fittings. This can be reduced using sodium bisulphate (pH Reducer). As with the pH level it is hard to estimate how much is required to reduce the alkalinity level therefore this process should be done a bit at a time to get use to how much is needed for your water supply. If the alkalinity level is too low then the water can become corrosive and uncomfortable to bathe in. The corrosion can also damage the heaters and pipe work resulting in it ultimately failing. This can be increased using sodium bicarbonate (alkalinity builder).

1 kg increases the alkalinity level of a 10,000 gallon pool by 12 parts per million. This can be added directly to the pool and dissolved using a pool brush.

Calcium Hardness
Calcium levels are usually a factor in tiled pools. If you have a tiled pool and are in a soft water area it is important that you keep sufficient calcium in the pool water. This is not a problem in hard water areas as the water supply will naturally contain enough calcium. If there is insufficient calcium in the water of a tiled pool the water will tend to dissolve the calcium in the grout making it soft. Eventually the grout will disappear leaving sharp edges which can cut the feet of bathers. In a tiled pool the calcium hardness should be kept above 200ppm. The calcium hardness can be increased by adding calcium chloride (calcium builder).

1 kg increases the calcium level of a 10,000 gallon pool by 12 parts per million.