CH255 PPM/pH Digital Controller

Sanitizer and pH Control Made Easy

CHEMTROL® CH255 PPM/pH Digital Controller introduces the new Sensor for Free Chlorine control. A microprocessor-based digital controller, designed to maintain both free chlorine (PPM) and water pH in Residential Pools and Spas, Commercial Pools and Spas, Hotels, Motels, Health Clubs, Apartments Buildings, Condo associations and Industrial Water Treatment.
Simplicity of installation, Compatible with all common sanitizers and oxidizers, ease of use and long-term reliability.

Standard Features

  • Easy to install, Simple to use
  • All Control Functions on Front Panel
  • Free Chlorine control
  • pH control
  • Separate Adjustable Setpoints
  • Separate Adjustable Alarms
  • Out-of-range alarms
  • Acid/Base Selector
  • Proportional Feed with Adjustable Bandwidth
  • Separate Adjustable Overfeed Safety Timers
  • Waterproof Cabinet with Clear Window Cover
  • 5-year Electronics Warranty

Precise and Reliable PPM Reading

The new Free Chlorine Sensor is a solid state sensor with a selective membrane that provides direct readings of Free Chlorine in water at concentrations ranging from 0.1 to 10 ppm (parts per million) or mg/l (milligrams per liter). These are true readings of Free Chlorine corresponding to the DPD #1 test.

A significant advantage of this PPM sensor is that it’s not affected by cyanuric acid (CYA) stabilizer and/or oxidizers, thereby assuring constant Free Chlorine levels at all times. Unlike other chlorine sensors on the market, this new sensor is easy to install and maintain and gives the operator precise and reliable control of Free Chlorine under the most difficult conditions. The PPM sensor is covered by a full 2-year warranty.

CH255 Specifications

Free Chlorine ControlAdjustable from 0.1 to 10.0 ppm (mg/l)
pH ControlAdjustable from 0.0 to 14.0
Free Chlorine SensorSolid state electrode with 3 m cable
pH SensorGlass electrode with 3 m cable
ReadoutsPPM (3 digits) and pH (2 digits) LEDs
Feed ModeManual, automatic, proportional
AdjustmentsSet-point, calibration, limits, feed rate
IndicatorsLEDs for feed mode, feed status, alarms
SafetyAudio, visual and remote alarms,
out-of-range limits and overfeed safety timers
CabinetPolystyrene 22 x 18 x 10 cm
Electrical230V or 24 VAC (specify)
Warranty5 years on electronic module

CH255 Installation

Unlike conventional amperometric or colorimetric sensors, the PPM sensor is easy to install and operate. It does not require a special pressure flow cell and/or expensive and expendable chemical reagents. And best of all, it’s maintenance free.

Installation of the CHEMTROL® CH255: For best operation, it is recommended to install the sensors on a bypass line with a Flow Cell Assembly (FCA) as shown on the schematic.

Flow Cell Assembly

The Flow Cell Assembly (FCA) includes a see-through cell with a plastic cover that regulates the flow of water and allows the operator to see the tip of the sensors.

The cell includes the following:

  1. two 1/2″ FPT fittings for the connections to the bypass line,
  2. two 1/2″ FPT fittings for mounting the sensors,
  3. a spigot for water testing,
  4. a bleed line to prevent air lock in the cell,

In addition it is also recommended to install a safety flow switch on the bypass line to prevent accidental feeding of chemicals.

CH255 Operation

The CHEMTROL® CH255 PPM/pH Digital Controller automatically maintains both sanitizer PPM and water pH in pools and spas.

All operating functions are clearly labelled and accessible from the front panel, with many safety and easy-reset features not found on other controllers:

  • pH calibration from 7 to 8,
  • PPM setpoint from 0.1 to 10.0 ppm or mg/l (or 0.01 to 2.0 optional),
  • pH setpoint from 7 to 8,
  • Chlorine and pH feed modes: off, manual, automatic,
  • PPM and pH proportional control bandwidth from 0 to 100% of the setpoint,
  • Chlorine high and low alarms from 400 to 900 mV,
  • pH high and low alarms from 4 to 10,
  • Chlorine overfeed safety timer from 0 to 999 minutes,
  • pH overfeed safety timer from 0 to 99 minutes.

To select a function, simply press PPM or pH and then the desired function.  The display shows the current function value.  Use the UP or DOWN arrows to adjust to the desired value.

Control Setpoints

The standard factory-set Chlorine control level is 1.0 ppm or mg/l, based on WORLD HEALTH ORGANIZATION (WHO) values for prevention of germs and bacteria. A range of 0.01 to 2.0 is also available for low chlorine level applications.

The standard factory-set pH control level is 7.5. Below 7.4, the water causes eye irritation and corrosion of equipment. Above 7.6, it also causes eye irritation plus water cloudiness, scaling, stains and reduced sanitizer efficiency.

To change the control levels, the operator presses PPM or pH and then SETPOINT. Use the UP or DOWN arrows to adjust the PPM and pH setpoints. To save the new setpoint value and exit, press SETPOINT again.

The controller then automatically activates the chemical feeders for sanitizer and acid (or soda) feed, as required to maintain the set PPM and pH levels – regardless of fluctuations in bather load, contamination and weather.  Like a thermostat maintaining a constant temperature, it prevents overfeeding or underfeeding, both of which are detrimental to good water quality.


When there is an alarm condition, the corresponding display flashes the alarm value:

  • PPM out-of-range,
  • pH out-of-range,
  • PPM overfeed,
  • pH overfeed.

The display stops flashing when the condition is corrected. To reset the overfeed timers, turn the feed mode to off and then back to Manual or Auto.


The ideal values are set as default values.  They can be adjusted by the operator at any time.  To reset all factory default values, press PPM and pH for 5 seconds.