Examples of techniques for monitoring and controlling the pH of a drilling fluid are disclosed. In one example implementation, a system may include a first sensor to sense a first pH-value and an associated first temperature of the drilling fluid prior to being heated by a drilling fluid heater and a second sensor to sense a second pH-value and an associated second temperature of the drilling fluid subsequent to being heated by the drilling fluid heater. The system may also include a controller comprising a memory having computer readable instructions and a processing device for executing the computer readable instructions. The computer readable instructions include receiving the first pH-value and first temperature from the first sensor, receiving the second pH-value and second temperature from the second sensor, and determining an amount of additive to add to the drilling fluid to maintain a desired pH-value at the second temperature.