Below shows the total alkalinity and pH over 19 reefs during a month in summer 2017. Note that the chemical properties are move distinct for the offshore values during the neap tide (half moon), when the residence time of the model is greater.
For details of carbon chemistry calculations see:
Mongin, M., M. E. Baird, B. Tilbrook, R. J. Matear, A. Lenton, M. Herzfeld, K. A. Wild-Allen, J. Skerratt, N. Margvelashvili, B. J. Robson, C. M. Duarte, M. S. M. Gustafsson, P. J. Ralph, A. D. L. Steven (2016). The exposure of the Great Barrier Reef to ocean acidification. Nature Communications 7, 10732.