"I have set the mode to AUTO, but the temperature still shows 25°C"

The MODE button in the main menu refers to the available built in PID controller, which activates and controls dosing equipment (i.e. chemical dosing pump).  

The temperature measurement is activated in the menu IN/OUT -> ANALOG -> TEMP.

Note: The temperature compensation can be activated for DIS and pH separately, in the Main menu > IN/OUT -> ANALOG -> DIS (or pH, respectively). The compensation uses the measured temperature if it is activated, or else the manual value set in the temperature menu.