Precipitations were conducted using a pH stat titrator using the constant composition technique between August 2020 and April 2022. Aragonite precipitation rates are estimated from the rate of titrant dosing. pH and DIC are used to estimate the seawater aragonite saturation state of each precipitation and, on occasion, the [HCO3-] and [CO32-]. Data were collected to determine how changes in the calcification fluids of calcareous organisms affect aragonite precipitation. Data were collected by Cristina Castillo Alvarez and interpreted by Cristina Castillo Alvarez, Nicola Allison, Adrian Finch, Kirsty Penkman, Roland Kröger and Matthieu Clog.