Pf, Mf Drilling Mud / Fluid Alkalinity Test & Lime Content
The alkalinity is important in Water Based Mud because it can affect the performance of some treating chemicals in the water-based fluid, especially if they require alkaline conditions for effective performance. Sodium  or  Potassium  Hydroxide  usually  provides the  hydroxyl  ions  (OH–)  for  adjusting  the  pH  of water-based fluids ( see also pH Test Procedures).
https://www.drillingmanual.com/2020/11/pf-mf-drilling-fluid-mud-alkalinity.html