MX2501 pH Data Logger

HOBO pH Logger

Easy data offload to mobile devices or Windows laptop via Bluetooth!

Onset HOBO pH and Temperature Data Logger Overview Video

HOBO® MX2501

pH and Temperature Logger
starting at just $695 USD!

The low-cost HOBO MX2501 pH and Temperature logger is designed for long-term monitoring of pH in estuaries, lakes, streams, rivers, and oceans. It communicates wirelessly via Bluetooth to the HOBOconnect app on your phone, tablet, or Windows computer, making logger setup, calibration, and data offload quick and easy, with no need for extra equipment or complicated calibration procedures.

Key Advantages

  • Data offload to your mobile device or Windows computer via Bluetooth
  • Guided pH calibration with the HOBOconnect app
  • Rugged PVC design for freshwater or saltwater deployments
  • Water detection feature for longer battery life
  • User-replaceable battery, pH electrode, and anti-biofouling copper guard

Easy Logger Setup and Data Management

Onset's HOBOconnect app makes it a snap to configure the HOBO MX2501 logger and manage collected data in the field.

You can view data in graphs, check the operational status of loggers, share data files and graph images, and store data in the cloud.

The HOBOconnect app is a free download from the Apple App Store, Google Play, or the Onset website for your Windows computer!

Guided Calibration via HOBOconnect

The HOBOconnect app's built-in guided calibration feature makes an otherwise difficult task a breeze, seamlessly walking you through the pH calibration process.

Simply follow the on-screen prompts and your logger is calibrated!

Rugged Design, Accurate pH Readings!

Built to be compact and rugged, the MX2501 logger has a replaceable pH electrode, an anti-biofouling copper guard, and a PVC housing, making it ideal for freshwater or saltwater environments. It also includes a battery-saving water detection feature for extended battery life and less maintenance.
HOBO MX2501 pH Logger Diagram
Frequently Asked Questions
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Can I download data from an MX2501 pH logger deployed in water?


No, the logger needs to be removed from the water to download the data.

Does the logger feature a user-replaceable electrode?



What type of pH electrode is used?


Plastic-bodied, double junction electrode with a Pellon® junction and gel reference electrolyte.

Can I calibrate with custom pH buffers?


No. The electrode is calibrated to 2 or 3 points using standard pH buffers (4, 7, and 10).

Is the calibration procedure the same for freshwater and saltwater applications?


The procedure itself is the same; however, some users deploying the loggers in saltwater may want to use a modified version of pH buffers that include chemicals (like Tris buffer) to make the hydrogen ion activity in the buffer more similar to its activity in saltwater