A system for monitoring percentage change in blood volume (ΔBV %) during dialysis treatment includes a sensor device configured to obtain hematocrit (Hct)-related measurements based on detecting light which has passed through extracorporeal blood of a patient undergoing the dialysis treatment; one or more controllers configured to: determine Hct values based on the Hct-related measurements obtained by the sensor device; determine ΔBV % values based on the determined Hct values; and generate a GUI having a ΔBV % plot based on the determined ΔBV % values; and a display device having a display configured to display the GUI having the ΔBV % plot. Zone indicators are provided on the display to distinguish between a first zone corresponding to a first ΔBV % profile, a second zone corresponding to a second ΔBV % profile, and a third zone corresponding to a third ΔBV % profile.