Glossary of Terms

Langelier’s Saturation Index. This is a calculation that helps operators determine if the water is out of balance, causing corrosion or scale and potential equipment damage. The NSPF Pool & Spa Operator Handbook will help people learn more about this calculation. Being proactive in water balance will ensure cost savings in the future.

Water balance is comprised of pH, calcium hardness, total alkalinity, temperature and TDS. When water is balanced, the Langelier saturation index is 0. Values above =0.3 lead to scaling and cloudy water, while values below -0.3 can cause corrosion of pool equipment and surfaces. If the water balance is not fixed in a timely manner, secondary effects can lead to rapidly declining water conditions that can affect the health of the water occupants.

Temperature is an important factor in water balance, mostly in extreme conditions such as spas and hot tubs with temperatures up to 104 degrees F or 40 degrees C. During winter conditions, temperatures as low as 30 degrees F or 0 degrees C can also affect the balance. Scaling can occur at higher temps; corrosion at lower temps.

pH is the intensity of acid or alkaline materials in the pool or spa water. Many things can cause pH levels to change, including rainfall, dust, covering a pool or pool additives used. A measurement below 7 is considered acid, while a measurement above 7 is base or alkaline. It is a significant factor in determining the water quality as it affects sanitizer levels, and how the human body reacts to the water.

The National Swimming Pool Foundation recommends maintaining a pH within an ideal range of 7.4 to 7.6. Chlorine range of 2.0 to 4.0 ppm and pH of 7.4 to 7.6 are common chemical parameters; however, the operator must follow local codes and regulations outlined by their individual state and local Departments of Health and Environment.

As the pH of water goes up, effectiveness of chlorine goes down, which gives a lower ORP. pH and ORP work conversely to one another, and are affected by other factors such as temperature, and TDS that can increase the negative impacts of unbalanced water.

Oxidation Reduction Potential (ORP) is the measurement of the oxidizing capacity present in water. ORP cannot be fooled by the effects of pH, total dissolved acids (TDS), stabilizers, and non-chlorine oxidizers. ORP values are used much like pH values to determine water quality. ORP measurements are used often to control disinfection with chlorine or chlorine dioxide swimming pools, potable water supplies, and other water analysis applications. Studies have shown that the life span of bacteria in water is strongly dependent on the ORP value.

The ORP probe or sensor is designed to indicate the oxidizing/reducing capability of pool water by measuring the electron activity of the water. The ORP test is expressed in millivolts (mV).

ORP probes are most commonly used as part of an automated chemical feed system. The ORP probe reading signals a controller to turn on or off chemical feeders.

A higher ORP reading equates to the sanitizer working more effectively.

Dual ORP output used on an automatic chemical controller is often chosen by hotels, condominiums, aquatic centers, schools, and public facilities because it allows for both a primary sanitizer, such as salt chlorine generator, with a secondary sanitizer, such as liquid chlorine, for rapid response to increased bather load. The second ORP sensor may also be used as a safety backup (second pump and tank) for liquid systems.

Total Dissolved Solids (TDS) 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. 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. 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.

Total Hardness refers to the amount of Calcium Hardness and Magnesium Hardness in pool or spa water. The calcium carbonate is what causes scaling thus, the critical measurement to monitor is the Calcium Hardness or CH. The ideal range for Calcium Hardness in swimming pools and spas is 200-400ppm, maximum 1000 for pools and waterparks. High levels of Total Hardness can cause scale to form, which can also cause pool filters or plumbing to clog and water to appear cloudy. Too soft – low in Total Hardness – can harm the pool and fixtures.

Total Alkalinity measures the amount of alkaline substances (primarily bicarbonates and carbonates) in your water. Total Alkalinity will measure the ability of the water to maintain a desirable pH so that your water chemistry is more easily controlled.

Cyanuric Acid (sometimes called Stabilizer or Conditioner) makes Chlorine more stable in the sun’s UV rays, which keeps the Chlorine from degrading. Levels can drop from an ideal range to zero in less than two hours without Cyanuric Acid. If the Cyanuric Acid levels are too high it can cause Chlorine to be inefficient. Cyanuric Acid is an important level to check in outdoor pools and spas. Ideal range is 30-50ppm. Should not exceed 40 ppm with ORP/pH control. Swimming pools that use Cyanuric Acid pose a unique challenge for pools automated with ORP controllers. ORP readings decline as the Cyanuric Acid levels increase.

Free Chlorine is the active available disinfectant in the water. Available Chlorine Content is the comparison of the relative amount of chlorine released into water for different chlorine disinfectants. This is the portion of the total chlorine that is not combined chlorine and is available as disinfectant (HOCI and OCI-). The terms “hypochlorous acid” and “chlorine” are often used interchangeably.

Total chlorine is the sum of free chlorine and combined chlorine. The level of total chlorine will always be higher than or equal to the level of free chlorine. The minimum recommendations for Free Chlorine at pools and waterparks is 1.0ppm; ideal is 2.0-4.0ppm, with a maximum of 5.0ppm. The EPA has set the maximum at 4.0 ppm however, many health codes set the maximum at 5.0 ppm or even higher.

Chloramines, one form of disinfection by-products (DBPs), are produced when disinfectants such as chlorine, used to protect against waterborne germs, react with impurities, including perspiration, body oils, urine and lotions introduced into the pool by swimmers. Chloramines cause foul odors, irritation of the skin, eyes and ears, and damage to indoor air handling systems. The common myth is “too much chlorine” when people smell chlorine; in fact, there may not be enough chlorine to reduce the chloramine levels.

Electrolytic chlorine generators (ECGs) are also often referred to as Salt Chlorine Generators. These devices generate chlorine by separating ordinary salt (NaCl) into its basic chemical elements through a process called electrolysis. The ocean’s salt content is approximately 35,000 ppm, human tears contain 4000 – 9000 ppm and human taste level of salt is approximately 3500 ppm. Most manufacturers advise the salt content in pool water to be 2500 to 3500 ppm. This mild saline solution is so low that it is almost impossible to taste the salt.

Supplemental Disinfection Systems (SDS) are used in commercial pools to mediate the inherent weaknesses of chlorine, providing a safer water experience for swimmers and pool employees. UV and Ozone are two key technologies that are implemented for SDS. UV and Ozone have been accepted as two leading technologies that can combat chlorine-resistant microorganisms such as Cryptosporidium, and have a kill rate of 99%.


Ozone is an efficacious antimicrobial oxidizer. When used in conjunction with low dose chlorine, the pool water quality and clarity is improved. These water quality improvements result from ozone’s potent and rapid oxidation of organic and inorganic compounds. Ozone is cost-effective, uses little energy, is safe for pool patrons, and causes no structural degradation to the pool, the facility, or HVAC system. An ozone disinfection system consists of two basic components that ensure optimum performance at the lowest operating cost:

1. The ozone generation system, which manufactures ozone gas.

2. The ozone management system, which efficiently dissolves the gas into the water while preventing off-gas of un-dissolved ozone.


UV sanitation systems eliminate chlorine-resistant microorganisms at a kill rate of 99.9%, similar to Ozone systems. The technology of UV systems is based on the production of UV radiation inside a light chamber by way of a powerful lamp, comparable to a standard fluorescent lamp. This lamp radiates a germicidal UV light that is used to disinfect pool and spa water. The UV system causes permanent damage to a number of microorganisms as the water circulates through the light chamber. The process attacks the microorganism’s DNA; protozoans, viruses and bacteria are unable to reproduce and remain inactive.

Chemical Controllers

Automated chemical controllers help reduce risk from recreational water illnesses. Chemical controllers use microprocessors as its basis for operation. These microprocessors are designed to recognize low sanitizer levels, low or high pH levels and make adjustments accordingly. Sophisticated systems will relay messages remotely. These systems can be very complex and have the ability to incorporate remote communication, log data on a continuous basis by means of digital readouts and sound alarms to warn when the chemical parameters are out of range. Monitoring chemical fluctuations is the main purpose; however, many controllers will actually advise the pool owner when the system water flow is low so backwashing can be initiated. Some controllers can send messages through pagers, PDA’s, smart phones or a combination of these. Chemical controllers should be calibrated regularly as the probes may become dirty or buildup with scale, requiring cleaning. Always follow manufacturers’ instructions when cleaning and calibrating these controllers

IPS Controllers
National Swimming Pool Foundation
Connie Sue Centrella, M.B.A
AquaChek Pool & Spa Test Strips
Beth Hamil, Del Ozone
American Chemistry Council

Key Terms:

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