Why is swimming pool water chemistry important?

Properly balanced swimming pool water chemistry is the single most important factor in maintaining a healthy and safe swimming environment. Proper water balance protects bathers and increases the life of the pool/spa equipment and components.

There are a number of factors that contribute to balancing pool water. pH, Total Alkalinity, Calcium Hardness, temperature, and Total Dissolved Solids (TDS).


pH has the most impact on bather comfort and properly balanced pool water. pH is the measurement of hydrogen ion concentration in water. The recommended pH of pool/spa water is slightly alkaline (7.2-7.4). To give you an idea of the human body and pH, human tears are about 7.5. The ideal range for comfort is 7.4 to 7.6. Acceptable range is 7.2 to 7.8.

pH is influenced by many factors including user waste, disinfectants, source water, air-borne debris, water balance chemicals, aeration, and evaporation. A lot of research is now going into the affects of urine on pool water chemistry, which builds disinfection by products and poorly affects air quality.

Controlling pH is necessary to assure bather comfort. It is also important in the efficiency of the disinfectant used, and the protection of pool components. Maintaining the proper level of Total Alkalinity is the method used to control pH. Testing before making any changes in the pH is the best approach, and if necessary then correcting the Total Alkalinity. Often, when the alkalinity is correct, the pH is correct.

Total Alkalinity is the amount of alkaline substances (primarily bicarbonates and carbonates) in the swimming pool water. It measures the ability of swimming pool water to resist changes in the pH. It acts as a buffer and an anchor to keep pH where it should be. Total Alkalinity will measure the ability of the pool water to maintain a desirable pH so that your pool water chemistry is more easily controlled.

Calcium Hardness

There is calcium present in the pool water naturally due to leaching from rocks and soil into the ground water. These rocks and soil contain calcium and magnesium. The ideal range for Calcium Hardness in swimming pools and spas is 200-400ppm, maximum 1000 for pools and waterparks. When it approaches 1000, it is very difficult to maintain pool water chemistry balance, pH and total alkalinity in the proper range. ((see Glossary)


The one factor in water balance that is not chemical is the pool water temperature. Temperature mainly plays a role in water chemistry balance when the temperatures are extreme. This is seen more with hot tubs/spas where high water temperature can be up to 104 degrees Fa or 40 degrees C. Pool water temperature can be a factor in maintain proper water balance of the chemicals. And in winter conditions equipment is also affected when temperatures drop as low as 32 degrees F or 0 degree C. In this situation you see more corrosive conditions.

Total Dissolved Solids (TDS)

The total weight of all soluble matter in the swimming pool water is the TDS. All dissolved matters that are added to the swimming pool water contribute to TDS. This includes salt, user waste, algicides, metal and stain control chemicals, clarifiers, defoamers, enzymes, wind-borne debris and swimming pool water balance chemicals. TDS is the measure of the total amount of dissolved matter in the water, such as calcium, magnesium, chlorides, sulfates and anything else in the water that will dissolve.

Total Dissolved Solids are the amount of residue that would remain if all the water evaporated or was removed. In some manner, it is the measurement of the age of the water. The National Swimming Pool Foundation recommends that an ideal level of TDS is not to exceed 1500 ppm above the startup level. Some health codes recommend partial water replacement when levels have risen by 2,000 or 3,000 parts per million (ppm) above the source water.

Out of Balance Water can cause:

  • Eye and skin irritation
  • Cotton” mouth for swimmers
  • Staining
  • Unsightly wrinkles in vinyl liner swimming pools
  • Interference with the efficiency of sanitizers
  • Corrosion of metals (pump seals, heaters, lights, etc.)
  • Cloudy water
  • Scale build up (white chalky appearance) on pool surface as well as inside filter and heater
  • Pitting and corrosion of gunite/concrete pools

Pool Water Chemistry that is out of balance should be tested. A high pH, high Total Alkaline or High Calcium Hardness will cause cloudy water.

What causes cloudy swimming pool water

The most common causes for cloudy swimming pool water are improper filtration, insufficient water circulation or flow rate, and poor pool water chemistry. There are many reasons the pool water is cloudy, but essentially, the cloudiness is the result of the presence of small particles (too small to be filtered) and are unable to be removed by oxidation. Swimmers contribute to the cloudy pool water by contaminating the swimming pool water with dry skin flakes, bacteria, residues on the skin, and cosmetics. This is one reason showers are recommended before entering the swimming pool. Other factors due to the environment contribute such as wind, rain, soil, vegetation that contribute to the establishment of these particles.

How to manage cloudy swimming pool water

Step 1: Check the filtration system. Clean the filter, and reestablish the proper flow rate.

Step 2: Establish proper swimming pool chemistry water balance.

Step 3: If the swimming pool water is still cloudy, likely there are microscopic suspended particles. In this case, water clarifier is needed.

Swimming Pool Water Clarifiers

Typically this product comes in liquid form, but solids are also available. It is important to read the directions and understand how the clarifier should be introduced to the swimming pool water. There are organic and inorganic (flocculants) clarifiers.

The most frequently used organic clarifier is called cationic clarifier, which has a positive charge. Cloudy water particles typically have a negative charge. When the cationic clarifier is added to the cloudy pool water, thus combining with the small negatively charged particles, the positively charged cationic clarifier bonds the small particles into larger particles. This makes it easier for the filter to trap the material. The result is less demand for disinfectant and more disinfectant available to keep the water healthy and sanitary. There are now pool water clarifiers that can help remove Cryptosporidium from the swimming pool water.

Inorganic water clarifiers are most commonly known as alum, or aluminum sulfate. Alum, when added to the swimming pool water, will form a gelatinous mass. This mass traps the microscopic particles which are suspended in the swimming pool water. Once this happens, the circulation system should be running for about 4 hours, allowing for proper mixing of the alum and the suspended particles. Then the circulation system is shut off for 12 to 24 hours. This process (flocculation) allows for the particles (now larger) to drop to the bottom of the swimming pool, where the flocculated particles are collected and vacummed.

Key Terms:

PH and ORP Controllers
Pool Chemsitry Controller
Water Park Chemistry
Automated Pool Chemical Controller