A fluid monitoring apparatus, including a circuitry housing containing circuitry for processing fluid sensing signals and responsively transmitting an output, with a sensor assembly adapted for mechanical and electrical coupling to the circuitry housing. The sensor assembly includes at least one sensing member arranged to respond to a fluid species of interest in the monitored fluid, for generation of an output. The apparatus includes at least one of (A) a printed circuit board adapted to engage the circuitry housing and to mechanically couple to the sensor assembly, (B) the sensor assembly including a base and sensing element removably connected to the base by press-fit coupling elements, and (C) the sensor assembly including a base and a sensing filament connected thereto, and a filament guard to protectively circumscribe the sensing filament.