Chemical Factors of Pool Operation
Proper chemical treatment is essential in order to prevent potential problems such as mineral scale and metal stain formation, cloudy water, or deterioration of the interior finish and the equipment.
Five factors affect water quality: pH, total alkalinity (adjusted as carbonate alkalinity), hardness (as calcium), total dissolved solids and sanitizer.
The pH, total alkalinity, and calcium hardness, as well as the temperature of the water, are used to determine the overall water balance. Water balance is the tendency of the water to be either “scale forming” or “corrosive/aggressive.” If you water has scale-forming tendencies this is usually related to high pH, high total alkalinity, and elevated calcium level (hard water) or a combination. Corrosive or aggressive water is commonly the exact opposite of the chemical factors involved in scale forming. This can destroy pool walls and cause corrosion of equipment.
To prevent these problems, it is essential to maintain proper chemical levels or values in the pool water.
pH refers to the level of activity of an acid or base in the water and is the most critical chemical factor in swimming pools It is measured on a scale from 0-14 with 7 being neutral. If you have a pH value between 0-7, this is considered acidic. A pH value of 7-14 is considered alkaline with 14 being the greatest base activity. Your pool water is best kept in the range of 7.2-7.8. If below 7.2 the water is considered to be corrosive and a pH higher than 7.8 will increase the tendency for cloudy water. Changes in the pH are caused by many factors, but the most common is the sanitizer used. Standardly chlorine is used in pools, and it comes in a variety of forms. For example, most tableted 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. A quality professional can work with you in understanding what types of sanitizer are best for your pool.
Total alkalinity is the ability of your pool water to resist a change in pH. The purpose is to help manage or control the pH in the pool. Total alkalinity acts as a buffer so when materials are added to a pool that would cause the pH to go up or down; the changes are controlled in order to prevent damages to your pool water balance. Remember that total alkalinity is best within the range of 80-120 ppm. When less than 80 ppm the water is considered aggressive, and the pH can quickly increase or decrease. If higher than 120 ppm, the water can become cloudy and scale forming with the pH increasing. To reduce total alkalinity, add small amounts of acid, either liquid or dry, over a period of several days instead of making significant adjustments rapidly.
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. TO
Decrease: Add small amounts of liquid or dry acid 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.
Calcium hardness refers to the sum of all the calcium dissolved in water. Having very high levels of calcium can be unstable and even more unstable if the pH or the total alkalinity rise above the normal levels. This can result in cloudy water and/or scale. Soft or low calcium water is considered aggressive and can remove calcium from plaster. If the pool is vinyl or fiberglass, the low calcium water may attack metal fittings and heat exchangers. This attack can result in the destruction of the fittings or pinhole leaks in the heater. When corrosion occurs, stains to appear on pool surfaces. Calcium content is best in the range of 100-400 ppm.
How to increase calcium hardness:
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
Total dissolved solids (TDS), is a lesser issue in fresh water, but pool water that has not been replaced over time, can accumulate TDS. TDS is essentially the sum of all materials dissolved in the water and normally run in the range of 250 ppm and higher. In general, when the TDS exceeds approximately 1500 ppm, problems may begin to occur. TDS can result in cloudy or hazy water at an elevated level. Therefore, it can be difficult in maintaining water balance, the reduction in sanitizer activity, and foaming. To reduce TDS, you need to drain some of the water and replace with fresh water. Unfortunately, sequestering agents do not help when high TDS levels are causing cloudy pool water.