Milwaukee MC125 PRO 2-in-1 Digital pH / ORP Controller

SKU: 9139-MC125~ea

Milwaukee MC125 PRO 2-in-1 Digital pH / ORP Controller

SKU: 9139-MC125~ea
Regular price $346.23 CAD
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Milwaukee MC125 PRO 2-in-1 Digital pH / ORP Controller

The Milwaukee MC125 PRO pH and ORP controller is designed for people looking to measure and adjust pH and ORP levels automatically with one simple controller. Simply set the pH and ORP parameters and let the Milwaukee pH Controller do the rest.  This item is preferred by people looking to dial in their testing program when they have an ongoing need to maintain levels.  Common uses are nutrient tanks, aquariums, pools, and spas. 

The controller offers an accuracy to ±0.2 pH with two-point manual calibration and ORP accuracy to ±5 mV.  It offers real-time pH and ORP measurements from 0.00 pH to 14.00 pH and -1000 mV to 1000 mV with a large LED for easy switching between parameters.  The controller provides a control range of 4 to 8 pH and -200 to 600 mV.

There are two dedicated relays for pH and ORP control to support a range of compatible devices.  Choose your device, including oxygen pumps, CO2-regulators, O3 ozonizers and other pH & ORP control devices, by simply plugging the device into the correct pH or ORP outlet. 

The controller comes with a complete mounting kit including two probe holders.


  • Fast, easy-to-read current results with large digital LCD readout
  • Accurate to ±0.2 pH and ±5 mV with the user selectable high/low set points
  • Simple two-point calibration for increased pH accuracy with manual trimmers for easy adjustment
  • Lab grade, gel-filled, double junction pH electrode and platinum ORP electrode included for low maintenance and high performance
  • 5-foot probe cables for extra flexibility when testing
  • 12 VDC power supply


  • pH Range: 0.00 - 14.00 pH
  • ORP Range: ± 1000mV
  • pH Resolution: 0.01 pH
  • ORP Resolution: ± 1 mV
  • pH Accuracy: ± 0.2 pH
  • ORP Accuracy: ± 5 mV
  • Set point pH: 4 to 8 pH
  • Set point ORP: -200 to 600 mV
  • Calibration: Manual 2 points pH
  • Alarm Active when reading is higher or lower than set point
  • pH Dosing Contact
  • 1 power plug for CO2 dosing
  • ORP Dosing Contact
  • 1 power plug for O3 dosing
  • pH Electrode: MA911B/2 (included)
  • ORP Electrode: MA921B/2 (included)
  • Environment: 0 to 50°C / 32 to 122°F; max RH 95%
  • Power Supply: 12 VDC adapter (included)
  • Power Drivers: 115 VAC, 2A, 60Hz or 230 VAC, 1A, 50Hz
  • Dimensions: 5.8 x 3.25 x 1.26 inches
  • Weight: 7.1 ounces

Milwaukee MC125 Manual


Properly maintaining pH and ORP probes will give fast, accurate results for longer. They are similar in design but there are some differences:

  • pH probes have a sensing bulb that loses sensitivity with age. All pH sensors have a limited life and response time gets longer with age.
  • ORP probes usually have a platinum electrode instead of a glass bulb. It has a long life, but residue build-up can affect response rates and accuracy.

Both electrodes also have a reference junction that can become clogged.  This causes slow and inaccurate results. Cleaning and keeping the probe hydrated will help prevent this.

The life of your pH probe can be extended in the following ways:

  1. Always store with the cap full of buffer or storage solution, not water.
  2. Clean your probe regularly by soaking in cleaning solution.
  3. Calibrate after cleaning and/or storage before testing to adjust for changes in the pH sensor.
  4. For the pH probe, gently stir in the sample for a faster result.
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