Sterling Pool Co., Inc.
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Commercial Swimming Pool Builder, Construction, & Equipment
         Phone: 410-667-1101     Email:     Fax: 410-252-2079 Fax   Home:         

Chemtrol 250 Digital Controller
(pH & ORP Controller)

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Chemtrol 250


A simple and inexpensive controller for:

bulletResidential Pools and Spas
bulletCommercial Pools and Spas
bulletHotels, Motels
bulletHealth Clubs
bulletApartments Buildings
bulletCondo Associations.
bulletMunicipal Pools


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:

bulletAdjustable Set Points
bulletAdjustable High and Low Alarms,
bulletAdjustable Overfeed Safety Timers,
bulletAdjustable Proportional Feed Control.

We carry all aspects of the system.

bullet Chemical Feed Pumps
bulletChemical Storage Tanks for the use of Sodium Hypochlorite
bulletCO2 Controllers for pH Control


bulletEasy to install
bulletSimple to use
bulletAll Control Functions on Front Panel
bulletSeparate Adjustable Setpoints
bulletSeparate Adjustable Alarms
bulletAcid/Base Selector
bulletProportional Feed with Adjustable Bandwidth
bulletSeparate Adjustable Overfeed Safety Timers
bulletWaterproof Cabinet with Clear Window Cover
bullet5-year Electronics Warranty
bulletToll-Free Technical Support


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.


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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.

Simple to Operate

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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:

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

bulletORP out-of-range,
bulletpH out-of-range,
bulletORP overfeed,
bulletpH 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

Part #





Chemtrol 250 Digital ORP and PH Controller


Call 410-667-1101


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Chlorinators & Chemical Feed Pumps

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Sterling Pool Co., Inc.     Contact  
P.O. Box 297                 
Cockeysville, MD  21030

Copyright 2014   Last modified: January 2014