A fluid treatment system, comprising: a housing defining a fluid flow channel through which fluid is flowable in a fluid flow direction from an inlet of the housing to an outlet of the housing; a first fluid treatment device positioned within the fluid flow channel between the inlet and outlet of the housing; a second fluid treatment device positioned within the fluid flow channel between the first fluid treatment device and the outlet of the housing; and at least one sensor module comprising a sensor probe positioned within the fluid flow channel between the first and second fluid treatment devices, the sensor probe comprising a plurality of hollow arms (122, 124) extending radially outward from a radially inward portion of the fluid flow channel to a radially outward portion of the fluid flow channel, each of the plurality of arms comprising a plurality of apertures facing a direction substantially opposite the fluid flow direction, the apertures being communicable in fluid receiving communication with a sample portion of fluid flowing through the fluid flow channel, wherein the sensor module further comprises at least one sensor communicable in sensing communication with fluid received through the apertures, wherein the at least one sensor module further comprises an extractor portion coupled to the sensor probe, the extractor portion comprising the sensor and the extractor portion being communicable in fluid receiving communication with the plurality of hollow arms of the sensor probe, and wherein the extractor portion comprises an outlet positioned between the second fluid treatment device and the outlet of the housing, the outlet of the extractor portion being communicable in fluid supplying communication with fluid flowing through the fluid flow channel of the housing. a housing defining a fluid flow channel through which fluid is flowable in a fluid flow direction from an inlet of the housing to an outlet of the housing; a first fluid treatment device positioned within the fluid flow channel between the inlet and outlet of the housing; a second fluid treatment device positioned within the fluid flow channel between the first fluid treatment device and the outlet of the housing; and at least one sensor module comprising a sensor probe positioned within the fluid flow channel between the first and second fluid treatment devices, the sensor probe comprising a plurality of hollow arms (122, 124) extending radially outward from a radially inward portion of the fluid flow channel to a radially outward portion of the fluid flow channel, each of the plurality of arms comprising a plurality of apertures facing a direction substantially opposite the fluid flow direction, the apertures being communicable in fluid receiving communication with a sample portion of fluid flowing through the fluid flow channel, wherein the sensor module further comprises at least one sensor communicable in sensing communication with fluid received through the apertures, wherein the at least one sensor module further comprises an extractor portion coupled to the sensor probe, the extractor portion comprising the sensor and the extractor portion being communicable in fluid receiving communication with the plurality of hollow arms of the sensor probe, and wherein the extractor portion comprises an outlet positioned between the second fluid treatment device and the outlet of the housing, the outlet of the extractor portion being communicable in fluid supplying communication with fluid flowing through the fluid flow channel of the housing.