Monitoring Swimming Pool Chemistry

When swimming is a popular activity during the hot summer months, swimming pools encounter an enormous deal of contamination. Bathers transfers contaminants such as sweat, dirt, oils, and sunscreen into the pool water, which revamps the pools chemistry. Other contaminants derive from the surrounding environment, such as leaves and insects.

Overall, contaminants categorize into three major categories as follows: physical, chemical, and biological. Physical contaminants, those in which you can observe tangibly, are filtered out by a mechanical system. Chemical contaminants, such as the compounds found within both sweat and sunscreen, are oxidized by chlorine. Furthermore, chlorine is used to destroy biological contaminants like: microorganisms living in the pool, such as algae and disease-causing pathogens.

The quality of the pool water gradually declines when the contaminated particles linger in the pool. Odor, discoloration, and algae growth may be apart of the potential consequences derived from this. Moreover, when pathogens are capable of surviving, bathers potentially experience infections and irritation. To assure that the pool water stays both safe and clean, it is critical to manage adequate chlorine levels as well as a high functioning filtration system.


How do pool operators recognize when the chlorine in the pool needs to be re accommodated? A classic pool chemistry monitoring system utilizes these two parameters: ORP and pH.

Pool Water ORP:
By reacting with the contaminants found in oxidation, chlorine decontaminates the pool water effectively. When this transpires, the results of these reactions generates either combined chlorine or chloramines. In order to understand if the chlorine concentration is high enough, the combined chlorine is not an effective sanitizer, therefore, the critical parameter is free chlorine.

Free chlorine describes how the chlorine that is available sanitizes the pool water. It exists in two basic chemical forms: hypochlorous acid (HOCl) and hypochlorite ion (OCl-). Additionally, hypochlorous acid is the most effective form of free chlorine for disposing the contaminants.

Some pool operators utilize the DPD test kits, which measures the given chlorine concentration. However, DPD – a chemical that reacts with chlorine to produce a red color – is it still unable to distinguish between the following:  free chlorine and combined chlorine. In addition to this, DPD cannot distinguish between hypochlorous acid and hypochlorite ion.

The effortless ways to precisely measure and adjust chlorine for thorough disinfection is by monitoring the ORP. The ORP, Oxidation Reduction Potential, readings are a measure of the sanitization activity of chlorine. Since HOCl is the form of chlorine, which is the most powerful oxidant, the ORP value is highly sensitive to fluctuations made within hypochlorous acid.

Pool Water pH:
Maintaining the proper pool water pH is essential for the bathers comfort, equipment maintenance, and chlorine functioning. The ideal pH for pool water is typically between 7.2 and 7.8. A pH value outside of this given range may cause issues, including the following:
• Bather discomfort due to skin and eye irritation (pH < 7.2 or 7.8 < pH)
• Decreased longevity of pipes and filters due to corrosion (pH < 7.2)
• Reduced sanitization activity of chlorine (7.8 < pH)

Chlorine Sanitization Activity:
The amount of chlorine needed to keep the pool water clean depends on countless contrasting factors. When more swimmers are in the pool, the concentration must be higher in order to adjust for heavier contamination. Heightened sunlight can diminish the chlorine effectiveness, while requiring higher concentrations for sanitation. The pH of the pools water impacts chlorine activity by affecting the equilibrium concentration of both the hypochlorite ion and hypochlorous acid. Hypochlorous acid concentration is reduced when the pool water pH is overly high. Consequently, chlorine is less effective at oxidizing contaminants, because it is not present in its most active form. The equilibrium reaction below demonstrates this effect:

free chlorine equilibrium reaction


A complete pool water monitoring system typically includes a pH sensor, an ORP sensor, and a controller. The controller adjusts the amount of chlorine and other chemicals added to the pool based off the inputs from the pH and ORP sensors. This type of set up, illustrated in more detail below, is ideal for automatic adjustments, as factors like sunlight and bather load which fluctuates monthly, daily, and even hourly.

pool water monitoring installation


Choosing the Right ORP Sensor:
For the most accurate ORP measurements, Sensorex recommends following industry standards for this type of ORP measuring surface.

  • Probes with standard platinum tips are recommended for regular chlorine pools.
  • Probes with gold tips are recommended for salt water chlorine pools.

Due to the large amount of plastic piping in typical pool systems, proper grounding is essential to prevent sensor inaccuracy and extended lifetime. If the system is not properly grounded, stray electrical currents will be attracted to the sensor.


Portable Measurements:
For pool technicians, who are responsible for multiple sites, a portable monitoring solution is essential. The SAM-1 Smart Aqua Meter enables technicians to monitor the pool pH and ORP with an iPhone, iPad, or Android device while on the go. Switching between the ORP and pH measurement modes takes only seconds for the user. The SAM-1 automatically recognizes the sensor type plugged into the headphone jack and loads appropriate calibration data. Notes and GPS locations can be appended to data, allowing monitoring at several sites in a single day. Data is easily exportable in both spreadsheet format and via email for data analysis and record keeping.

Direct Fit Replacements:
If your pool chemistry monitoring system has already been operating for some time, you may need replacement sensors. Sensorex offers a range of direct fit replacement sensors for pool and spa applications. To find the right sensor to retrofit your system, use our pool sensor manufacturer cross reference guide.


Monitoring pH and ORP is critical to maintaining safe, clean pool water chemistry. Key benefits include:

  • Ensures bather comfort and water cleanliness
  • Verifies sanitization activity of chlorine
  • Reduces damage to pipes due to corrosion at low pH
  • Automatically controls and adjusts chlorine and other chemicals

Swimming Pool pH Sensors

Swimming Pool ORP Sensors