The main objective of this investigation is to develop non-biological surrogate indicators for assessing disinfection efficiency in ozone contactors. The indicators selected are fluorescent-dyed microspheres. These commercially available particles are manufactured from polystyrene and dyed with various fluorescent chemicals. This paper presents considerations on microsphere selection and fluorescence measurement tool assessment, mathematical models representing dye decay kinetics, and results of semi-batch fluorescence decay kinetic studies. A flow cytometry method to assess microsphere inactivation kinetics is also proposed.