A method for characterizing deposits from a fluid in a fluid flow system comprising: operating a first resistance temperature detector (first RTD) (102,202,302,402,502) in a heating mode of operation in order to heat the first RTD (102,202,302,402,502) to a corresponding first characterization temperature; periodically switching the first RTD (102,202,302,402,502) between the heating mode and a measurement mode in order to measure the temperatures of the first RTD (102,202,302,402,502), wherein periodically switching between the heating mode and the measurement mode comprises rapidly switching from the heating mode to the measurement mode and back to the heating mode so that, while in the measurement mode, the temperature of the RTD (102,202,302,402,502) does not significantly change; observing, via a controller, changes in the thermal behavior of the first RTD (102,202,302,402,502) in one or both of the heating mode and the measurement mode, wherein observing changes in the thermal behavior of the first RTD (102,202,302,402,502) comprises, measuring the rate at which the temperature of the first RTD (102,202,302,402,502) increases due to the operating of the first RTD (102,202,302,402,502) in the heating mode by switching between the measurement mode and heating mode; characterizing a level of deposit from the process fluid onto the first RTD (102,202,302,402,502) based on the observed changes, wherein characterizing the level of deposits from the process fluid onto the first RTD (102,202,302,402,502) comprises associating the rate of temperature change of the first RTD with a level of deposit from the process fluid; and performing a corrective action based on the characterized level of deposit on the first RTD (102,202,302,402,502); wherein the corrective action comprises adding or increasing an amount of biocide in the process fluid. operating a first resistance temperature detector (first RTD) (102,202,302,402,502) in a heating mode of operation in order to heat the first RTD (102,202,302,402,502) to a corresponding first characterization temperature; periodically switching the first RTD (102,202,302,402,502) between the heating mode and a measurement mode in order to measure the temperatures of the first RTD (102,202,302,402,502), wherein periodically switching between the heating mode and the measurement mode comprises rapidly switching from the heating mode to the measurement mode and back to the heating mode so that, while in the measurement mode, the temperature of the RTD (102,202,302,402,502) does not significantly change; observing, via a controller, changes in the thermal behavior of the first RTD (102,202,302,402,502) in one or both of the heating mode and the measurement mode, wherein observing changes in the thermal behavior of the first RTD (102,202,302,402,502) comprises, measuring the rate at which the temperature of the first RTD (102,202,302,402,502) increases due to the operating of the first RTD (102,202,302,402,502) in the heating mode by switching between the measurement mode and heating mode; characterizing a level of deposit from the process fluid onto the first RTD (102,202,302,402,502) based on the observed changes, wherein characterizing the level of deposits from the process fluid onto the first RTD (102,202,302,402,502) comprises associating the rate of temperature change of the first RTD with a level of deposit from the process fluid; and performing a corrective action based on the characterized level of deposit on the first RTD (102,202,302,402,502); wherein the corrective action comprises adding or increasing an amount of biocide in the process fluid.