Advantages of Optical pH Sensor Technology with AquapHOx Underwater Loggers and Transmitters

Updated: May 10


Optical pH sensors by PyroScience offer affordable, robust and reliable pH monitoring in global oceanic environments. These sensors are based on a unique optical REDFLASH technology and provide a viable alternative to the traditional pH measurement devices such as pH electrodes.


Similar to the tried and tested oxygen sensor, the REDFLASH technology in pH sensors utilizes special luminescent and reference indicators that are excited with orange-red light and produce NIR emissions based on the sample’s acidity level that is recorded and logged according to the selected sampling interval. These pH sensors feature outstanding low cross-sensitivity to ionic strength in harsh marine conditions as well as exceptional selectivity at defined pH ranges. There is also two calibration options. In addition to total scale, which is considered the industry standard for seawater measurements, NIST scale calibrated pH sensors are also available.


The great variety of sensor formats compatible with AquapHOx systems (view options here) allows for the maximum flexibility of testing setups from freshly collected water samples brought to research vessels to in situ deployments that help investigate distributions of key oceanographic parameters (oxygen, pH and temperature) and their dynamics at great water depths down to 4,000 meters.

AquapHOx deep sea logger with pH sensor cap is being deployed as part of benthic lander.

With optical pH sensors from PyroScience, high-selectivity, reliable total scale ocean measurements with negligible impact of salinity (which is a typical challenge to their

electrodes counterparts) can be performed even under the most challenging hard-to-reach deep-sea conditions. That is why Dr. Andrea Kealoha, a marine oceanographer from Hawaii University chose to test the AquapHOx-LX prototype as part of the “Guardians of the Ocean” expedition with Trailblazer and Discover the Oceans back in January 2021.



Dr. Andrea Kealoha and crew member are reading installation for AquapHOx-LX (on her elbow)

Dr. Kealoha specializes in studying climate change impact on coral reefs as well as threats to ocean and freshwater resources. Her research group deployed the AquapHOx-LX underwater logger equipped with a pH sensor cap (PHCAP-PK8T-SUB) off of Hawaii's Kona coast with the goal of learning how the corals survive in the acidified, really cold environments down to 4,000 meters deep. This was the first time this type of data collection was performed in this area giving start to the groundbreaking deep water coral resilience research.


PHCAP type sensors represent a new generation of optical pH sensors that are highly robust against mechanical impact, do not require a reference electrode and are ideal for long-term monitoring.


Ohio Lumex is a solo distributor of PyroScience sensors in the US and Canada.


Contact us for more details about these systems and their suitability for your applications.


[Pictures credits: Discover Our Oceans LLC]