Fig. 4 also shows a lack of data in the pH range of 5.2–6.5, indicating that stable conditions for the acidification of SDW did not occur in this range. This result is even more evident when considering that the initial pH was set to 6.0 for all vessels. This fact is probably related to both the production of carbon dioxide during SDW acidogenesis and the unstable equilibrium of carbonates at pH values close to 6 [35].