a fluid treatment apparatus comprises a fluid inlet 12 and outlet 13 , a granular filter media 15 arranged to filter fluid flowing from the inlet 12 to the outlet 13 and a device 14 arranged to vibrate or agitate the media as fluid flows through the media between the inlet 12 and outlet 13 . vibrating or agitating the granulated media in this way produces a grinding effect which serves to kill any micro - organisms caught in the filter by rupturing their cell walls .