A self-cleaning oxidation-reduction potential (“ORP”) probe system includes an ORP electrode (11), a flow cell (12) surrounding the ORP electrode, and a plurality of cleaning beads (17) contained in the flow cell in a manner in which they are free to contact the ORP electrode when fluid is passed through the flow cell. The self-cleaning probe system may also or alternatively include a pH probe electrode, or another fluid-testing probe, in the flow cell.