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A simple and inexpensive controller for:

  • Residential Pools and Spas
  • Commercial Pools and Spas
    • Hotels, Motels
    • Health Clubs
    • Apartments Buildings
    • Condo Associations.
  • Industrial Water Treatment.
  • Compatible with all common sanitizers and oxidizers.

NOTE: ORP sensors are not recommended with electrolytic chlorine generators..


The CHEMTROL® 250 is a microprocessor-based digital controller designed to maintain both sanitizer ORP (oxidation-reduction potential or Redox) and water pH in high-end residential pools, small commercial pools and spas and light industrial applications.

Designed for affordability, simplicity of installation, ease of use and long-term reliability, it includes features normally not found on this type of controller, such as:

• adjustable setpoints,

• adjustable high and low alarms,

• adjustable overfeed safety timers and

• adjustable proportional feed control.



The CHEMTROL® 250 controller is based on 20+ years of experience in pool and spa automation with over 25,000 installations worldwide. Featuring a 5-year electronics warranty, it actually pays for itself in 1 to 2 years through cost savings in operating and maintenance expenses.

Savings continue to accrue from the more efficient use of chemicals, avoiding over- and underfeeding, and from lower labor costs for water testing and repairs of damaged equipment. In particular, commercial operators save on specialty chemicals, customer complaints and health department shutdowns.


Installation of the CHEMTROL® 250 is as easy as 1-2-3.
  1. CONTROLLER - Connect the controller to the 110 or 230V output of the Timer in parallel to the recirculation pump.  This will prevent accidental feeding of chemicals when the pump is not running. Make sure to follow the electrical code.
  2. SENSORS - Install the ORP and pH sensors on the recirculation line or on the optional bypass line.  The two sensors can be mounted directly on the main recirculation line with 2" PVC tees, as shown on the schematic.  For recirculation lines over 2" in diameter lines, the sensors should be mounted on a 1/2" bypass line.
  3. CHEMICAL FEEDERS - Connect the chemical feeders to the 110 or 230V controller outputs, according to the manufacturer's instructions, making sure to inject the chemicals downstream of the sensors.  For a bromine or chlorine erosion feeder, install a corrosion-resistant solenoid valve on the intake line of the feeder.  The controller is compatible with most ozonators and electrolytic generators.

Flow Cell Assembly

For best operation, it is recommended to install the sensors on a bypass line with a Flow Cell Assembly (FCA) as shown below.
The 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 switch on the bypass line to prevent accidental feeding of chemicals.


The CHEMTROL® 250 ORP/pH Digital Controller automatically maintains both sanitizer ORP (oxidation-reduction potential or Redox) and water pH in pools and spas.

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

  • pH calibration from 4 to 10,
  • ORP setpoint from 400 to 900 mV,
  • pH setpoint from 4 to 10,
  • ORP and pH feed modes: off, manual, automatic,
  • ORP and pH proportional control bandwidth from 0 to 100% of the setpoint,
  • ORP high and low alarms from 400 to 900 mV,
  • pH high and low alarms from 4 to 10,
  • ORP overfeed safety timer from 0 to 999 minutes,
  • pH overfeed safety timer from 0 to 99 minutes.

To select a function, simply press ORP 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.


The standard factory-set ORP control level is 700 mV, based on WORLD HEALTH ORGANIZATION (WHO) and NATIONAL SPA AND POOL INSTITUTE (NSPI) values for prevention of germs and bacteria.

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 ORP or pH and then SETPOINT. Use the UP or DOWN arrows to adjust the ORP 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 ORP 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:

  • ORP out-of-range,
  • pH out-of-range,
  • ORP 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 ORP and pH for 5 seconds.



Adjustable from 400 to 900 mV


Adjustable from 4.0 to 10.0


Platinum electrode with 10-ft (3 m) cable


Glass electrode with 10-ft (3 m) cable


ORP (3 digits) and pH (2 digits) LEDs


Manual, automatic, proportional


Setpoint, calibration, limits, feed rate


LEDs for feed mode, feed status, alarms


Audio, visual and remote alarms
Out-of-range limits and overfeed safety timers


Polystyrene 9x7x4 in. (22x18x10 cm)


110V, 230V or 24 VAC (specify)


PVC tees for 1-1/2" or 2" line


5 years on electronic module
1 year on all other parts


12x12x12-in (30x30x30 cm) carton
8 lbs (3 kg) without pumps
16 lbs (6 kg) with 2 chemical feed pumps


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