Pool water monitoring – DPD explained

Category: Pools | Tags:


As one of the oldest and most common forms of disinfection, chlorine improves water quality by destroying disease-producing microorganisms, and by reacting with other organic and inorganic substances.
Chlorine levels must be actively monitored to ensure sufficient chlorine is present for disinfection, as well as to control adverse effects such as taste, odor, and potential reactions with organic matter to form harmful disinfection by products.
Chlorine is a strong oxidising agent that destroys mostly organic pollutants and bacteria and can combine with nitrogen containing compounds, forming chloramines. — > Combined Chlorine
When dosing chlorine for disinfection, only a portion of the dosed chlorine remains active to actually continue the disinfection process. –->Free Chlorine

DPD Colorimetric method

DPD method is the most commonly used procedure to determine free chlorine residuals in water. The DPD indicator immediately reacts with free available chlorine—hypochlorous acid or hypochlorite ion to form a variety of shades of magenta color, which are proportional to the chlorine concentration.
US Environmental Protection Agency, EPA accepted colorimetric N,N-diethyl-pphenylenediamine (DPD) method.
The resulting chemical reaction causes a magenta color to form in the presence of chlorine. The color intensity is proportional to the concentration.
Blank free
chlorine sample
Low chlorine
within range
High chlorine
within range
above range
(bleaching effect)
The color intensity is measured photometrically (light source at a specific wavelength and a photodetector) and converted to chlorine concentration, in mg/L, which is displayed on the front panel.
Why Free Chlorine measurement is so important?
residual or
Therefore if we test water and find that there is still some free chlorine left, it proves that most dangerous organisms in the water have been removed and it is safe for bathers.


Portable Photometer
for pH, Alkalinity,
Free and Total Chlorine
and Cyanuric Acid
  • waterproof
  • designed with an innovative optical system that offers superior performance in accuracy, repeatability, and the amount of time that it takes to do a measurement
  • extremely user friendly with a tutorial mode that walks the user graphically, step by step, in performing a measurement
  • backlit dot matrix LED allows the use of virtual keys making operation of the meter very intuitive
  • The casing offers IP67 waterproof protection and floats

CAL Check™ functionality

Hanna’s exclusive CAL Check feature allows for performance verification and calibration of the meter using NIST traceable standards. Our CAL Check standard vials are developed to simulate a specific absorbance value at each wavelength to verify the accuracy of subsequent readings. The CAL Check screen guides the user step-bystep through the validation process and user calibration.
Multiple measurement methods
Users can select the use of powder reagents supplied in packets or the use of low cost liquid reagents supplied in a dropper bottle. Built-in reaction timer Waiting the proper reaction time is of key importance when performing colorimetric measurements. The countdown timer displays the time remaining until a measurement will be taken, ensuring consistent results between sample measurements and users.
6.5 to 8.5 pH
0 to 500 mg/L (as CaCO₃)
Free Chlorine
0.00 to 5.00 mg/L (as Cl₂)
Total Chlorine
0.00 to 5.00 mg/L (as Cl₂)
Cyanuric acid
0 to 80 mg/L (as CYA)

* Reagents sold separately

Available as C version
HI97104C includes photometer, CAL Check cuvette A, CAL Check cuvette B for free and total chlorine (powder and liquid), CAL Check cuvette B for pH, CAL Check cuvette B for cyanuric acid, CAL Check cuvette B for alkalinity, sample cuvettes (2), sample caps (2), plastic stoppers (2), 1.5V AA batteries (3), cuvette wiping cloth, scissors, instrument quality certificate, instruction manual and HI7101414 rigid carrying case.


Pool Line
Free Chlorine Checker® HC

Handheld Colorimeter

  • Easier to use and more accurate than chemical test kits
  • EPA approved DPD method
  • Large, easy-to-read digits
  • Dedicated to a single parameter
  • The Checker®HC easily fits into the palm of your hand or pocket
  • Use for quick and accurate on-the-spot analysis
  • Single-button operation: zero and measure 

and continuous

PCA 310 ● PCA320 ●PCA330 ● PCA340

PCA 310 ● PCA320 ●PCA330
● PCA340

Chlorine, pH, & ORP Control

The Hanna PCA300 series chlorine analyzers continuously monitor, control, and adjust chlorine content and pH of a sample stream. From drinking and wastewater treatment to pool and spa sanitation, monitoring chlorine levels has an important bearing on public health as well as ROI and efficiency for heating system and industrial applications.
  • 4 models available for monitoring chlorine, pH, and ORP levels.
  • Separate alarms can be set for chlorine, pH, ORP and temperature controls.
  • User-friendly interface simplifies setup and maintenance.
  • DPD Colorimetric method

DPD Colorimetric method

The PCA Analysers uses DPD Colorimetric method. The technology used by the PCA for chlorine measurement is the same as that found in portable and benchtop colorimeters providing for consistent results when performing process verification with one of those types of meters.
The sampling interval for chlorine measurement is adjustable from 3 to 90 minutes.
The PCA has a dosing relay for the addition of chlorine by a dosing pump or chlorine generator when a reading is below the programmable set point.

Amplified pH electrode

The PCA Family also uses the HI1005 amplified pH electrode with a built in pt100 temperature sensor and matching pin to measure both pH and temperature. The built in amplifier and matching pin provide for exceptional performance against any electrical noise generated by pumps and motors.

Analog output

The PCA340 features two selectable 0-20 or 4-20 mA signal output that are scalable for the transmission of readings to external recording devices. The analog outputs can also be set for dosing and used with dosing pumps that accept a 4-20 mA analog input. The analog outputs can be used for any of the three measured parameters.
Nives Vinceković Budor
With Great Product Come Great Results





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