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5th International Symposium on the Ocean in a High CO2 World, 13-16 September 2022, Lima, Perú, The pH spectrophotometric method is the gold standard to measure pH in the ocean and detect ocean acidification trends due to the anthropogenic carbon uptake from the atmosphere into the ocean. The pH method has an accuracy of about 0.003 and a precision of about 0.0004 pH units. The method has evolved since the 1990s when defined using manual approaches and unpurified dyes to currently automated methods using expensive and cumbersome to obtain purified dyes. From a collection of about 300 paired measurements of unpurified and purified pH measurements along with DIC and TA from natural samples in the Eastern North Atlantic and Mediterranean Sea we find that contrary to expected, unpurified and purified pH measurements calculated with the proper corresponding functions agree to within 0.003 pH units for waters with pH >7.95, while waters with lower pH, calculated unpurified pH is higher than purified pH. Applying the purposed correction from unpur to pur pH as explained in the literature is not straight forward, the community risks for an incoherence in the pH time series. Clearly, we need a definition and evaluation of the unpur to pur correction on real seawater samples by different labs, and look for a consensus agreement on seawater pH definition (scales!, ionic model), metrology, and on the Standard Operational Procedure, where loose issues are still present