Reflex Fillguard Mini sensor for monitoring the capacity status of Fillsoft Zero demineralization cartridges when treating fill and top-up water for heating systems. It is particularly suitable for use with Reflex Fillsoft Zero to implement low-salt operation according to VDI 2035. It has a measuring cell with a 1/4" external thread for installation directly in the head of the Fillsoft housing. Fillguard Mini constantly measures the electrical conductivity of the demineralized water and indicates the degree of demineralization via flashing LEDs: Green LED - electrical conductivity less than 10 SS/cm; Yellow LED - electrical conductivity 10-100 SS/cm; Red LED - electrical conductivity greater than 100 SS/cm