This data set reports the growth rate and carbonate chemistry variables (initial and final) for a single-strain culture study on the unicellular diazotrophic cyanobacteria, Crocosphaera watsonii. C. watsonii was cultured at a six different artificial seawater medium pH levels (pH free range = 7.2 - 8.8) in triplicate to investigate the growth rate response to ocean acidification. Growth rates were highest between pH ~7.9 and 8.2 and no growth detected in 2 of 3 replicates at the lowest pH level. This indicates an optimum curve response pattern of this cyanobacteria species to seawater pH, similar to that already observed in calcifying haptophytes.