This data set is a combination of data from both laboratory experiments where carbonate chemistry parameters from both were used to calculate aragonite saturation state (omega) and the extended calcification substrate inhibitor ratio (ESIR). These mean values from each experimental treatment are plotted with mean values for calcification in each experimental treatment from both experiments to understand whether omega or ESIR can predict calcification more accurately in the Baltic Sea and whether Baltic Sea mussels can cope with lower ESIR and Omega values than fully marine populations.