An eddy covariance system, known as ECHOES, was deployed at three sites offshore of Key Largo, Florida during June 2018. The ECHOES systems logged the three-dimensional velocity, depth, O2 optode, pH sensor, and triaxial Inertial Measurement Unit. A separate frame at each site contained a photosynthetically active radiation (PAR) sensor and a Seabird SeapHOx, measuring salinity, temperature, depth, O2, and pH. This dataset contains pH, temperature, salinity, and oxygen data recorded by the SeapHOx sensor.