Water Chemistry

Swimming pool maintenance is more than simply adding sanitizer, adjusting the pH and running a filter.

Proper chemical treatment is necessary to prevent problems such as mineral scale and metal stain formation, cloudy water, or deterioration of the interior finish and the equipment.

Effects of bad water chemistry

Five factors affect water quality: pH, total alkalinity (adjusted to carbonate alkalinity), calcium hardness, total dissolved solids, and sanitizer. Temperature is also a factor that impacts water chemistry balance, but in most cases is not considered a controllable factor.

The pH, carbonate alkalinity, calcium hardness, total dissolved solids, and temperature of the water, are used to determine the overall water balance. Properly adjusting these parameters allows you to keep the water balanced, in order to avoid the tendency of the water to become either “scale forming” or “corrosive/aggressive.” Scale-forming tendencies are usually related to high pH, or elevated levels of alkalinity, calcium hardness, total dissolved solids, or a combination of these. Conversely, corrosive/aggressive deterioration is usually related to low pH, or low levels of carbonate alkalinity, calcium hardness, total dissolved solids, or a combination of these. . Corrosive/aggressive water can also destroy pool tile grout, metal light rings, heaters, and pool equipment.

Low Carbonate Alkalinity

Low ORP Readings

Sanitizer Issues

Scaling or Staining Issues

Filtration Issues

Degradation of the Interior Finish

Algae Growth

Prevention

Maintaining proper service and proper water balance (chemical levels or ‘ranges’) is essential in the prevention of these issues. Water chemistry should be maintained in accordance with APSP ‘Balanced Conditions’. The following parameters are recommended:

  • pH should be kept within the range of 7.2 – 7.8. At a pH below 7.2, the water is considered to be ‘aggressive’, and a pH above 7.8 is considered to be ‘scaling’, and has the tendency to precipitate minerals and/or metal causing scaling or staining of the surface.
  • Carbonate Alkalinity should be kept within the range of 80 – 120 ppm. To Adjust Alkalinity: Increase: 1.5 pounds of Alkalinity Increaser or Sodium Bicarbonate will increase the total alkalinity of 10,000 gallons of pool water by 10 ppm. Decrease: Add small amounts of liquid or dry acid (diluted or dissolved) once each day until desired level is reached. In general, about 2 pounds of dry acid will reduce total alkalinity of 10,000 gallons of pool water by 10 ppm. For minor adjustments, do not add more than one pound of dry or one pint of liquid to 10,000 gallons of water per day. Remember, do not add ANY acid if pH is less than 7.2.To reduce total alkalinity, add small amounts of acid, either liquid or dry (dissolved in a bucket of water), over a period of several days instead of making significant adjustments rapidly.
  • Calcium Hardness content should be kept within the range of 200 – 400 ppm . A low calcium hardness level can cause the deterioration of the interior finish and tile grout. To increase calcium hardness, add calcium chloride. One pound of calcium chloride will increase the calcium hardness of 10,000 gallons of water by 10 ppm.
  • Total Dissolved Solids should not exceed 1500 ppm (above the source water TDS). If higher than 1500 ppm, the water has the tendency to precipitate minerals and/or metal causing scaling or staining of the surface For salt water pools, the TDS should not exceed 1500 ppm above the source water TDS plus the added salt. The water can also become cloudy. It is recommended to drain some of the water and replace with fresh water. Alternatively, in certain regions of draught or water restrictions, there are methods to reduce or remove metals, minerals, and dissolved solids through filtration.
  • Cyanuric Acid should be kept within the range of 30 – 50 ppm. It is recommended to periodically drain some of the water and replace with fresh water, so that cyanuric acid levels do not build up.

 

Additional Resources:

For detailed technical information on water chemistry view our references and resources page.

Test Water Regulary

Invest in filtration system

NPC Member Advertisements

Experienced pool professionals understand that their performance is primarily measured by how well they can prevent problems and keep water looking inviting, not on how well they solve recurring problems. Recurring issues can be avoided by proper maintenance and understanding the pool water chemistry.