Water Quality
Proper chemical and mineral treatment of water is important to prevent problems such as:
scale and stain formation,
colored or cloudy water,
corrosion of pool surfaces and equipment and to assure
proper performance of the sanitizer being used.
The five chemical factors that affect water quality are:
pH 7.2-7.8 water balance
Total Alkalinity 80-120 ppm water balance
Calcium Hardness 100-400 ppm water balance
Stain Producing Minerals
Total Dissolved Solids (TDS) 250-1500 ppm
pH , power of Hydrogen
pH refers to the degree of activity of an acid or base in the water. It is measured on a scale from 0 to 14 with 7 being neutral. A pH value between 0 and 7 is considered acidic with 0 being the greatest acid activity and getting weaker as it approaches a value of 7. A value of 7 to 14 is considered basic with 14 being the greatest base activity. Ideal pool water pH is in the range of 7.2 to 7.8.
When pH lingers below 7.0, the water is considered to be corrosive. This means etching of plaster and metals in equipment such as heat exchangers may result. It is more difficult to keep (stabilize) chlorine in the pool because while more effective as a sanitizer at the low pH, chlorine is also much less stable resulting in the consumption of larger quantities of chlorine than would be used at normal pH levels.
On the other hand, maintaining the pH higher than 7.8 will increase the tendency to form scale or cloudy water. Calcium, the major component in scale, is a relatively unstable mineral and when the pH is high, the calcium is not as soluble and it will tend to precipitate or “fall out” of solution resulting in cloudiness or scale. High pH will also reduce chlorine effectiveness resulting in the need to maintain higher chlorine levels to achieve maximum sanitization.
To increase low pH, sodium carbonate, pH UP or soda ash, is added to raise the pH. To decrease pH add pH DOWN or liquid acid (muriatic acid) or dry acid (sodium bisulfate).
The most frequent cause of change in the pH of pool water is the sanitizer used. Of the sanitizers typically used in pools, chlorine is the most common. Chlorine comes in a variety of forms and varies widely in pH. For example, stabilized forms of chlorine have a very low pH and will tend to lower pH over time, while liquid chlorine is very high in pH and will tend to raise pH values. Changes in pH due to sanitizers or other factors can be minimized by controlling alkalinity.