This dataset contains only the sensor data and only from the forereef mooring on the north shore. Full carbonate chemistry data derived from water samples where available are in a separate dataset. Sensor data from other locations are in a separate dataset. Near continuous measurements of seawater pH are made at two locations on the north shore of Moorea. On the fore reef, instruments are attached to a mooring cable at 10-m depth at LTER0. On the back reef, instruments are bottom-mounted at a location approximately 400 m landward of the reef crest at LTER0, such that pH of the same water mass is measured at both locations as water moves onto the reef crest and across the back reef (Hench et al. 2008). One SeaFET instrument and one SAMIpH instrument are deployed at each location. Measurements of pH by the SeaFETs are made every 30 minutes; pH measurements by the SAMIs are made every hour. SeaFET data (on the total pH scale) are output using both a constant salinity value (35 PSU) and using salinities measured in situ, if available. SeaFETs are calibrated using independent measures of pH from water samples taken adjacent to the instruments prior, during, and after deployment (using the m-cresol purple method). SAMIs are returned to the manufacturer each year for calibration. This material is based upon work supported by the U.S. National Science Foundation under Grant No. OCE 16-37396 (and earlier awards) as well as a generous gift from the Gordon and Betty Moore Foundation. Research was completed under permits issued by the French Polynesian Government (Délégation à la Recherche) and the Haut-commissariat de la République en Polynésie Francaise (DTRT) (Protocole d'Accueil 2005-2019). This work represents a contribution of the Moorea Coral Reef (MCR) LTER Site.