Ozone Contact and Redox Control

Ozone treatment in aquaculture is dosed and verified through oxidation-reduction potential (ORP, measured in mV), with target redox values typically 250–300 mV for bacterial control in seawater systems and 300–350 mV where aggressive disinfection of recycled water is required. Because ozone decays within minutes, effective systems provide a true contact chamber giving 2–5 minutes of hold time at the target residual, not just injection at the pump inlet. ORP is the practical proxy for dissolved ozone: at 300 mV in full-strength seawater the instantaneous ozone residual is usually below 0.1 mg/L, yet oxidation of organics and microflocculation of fine particles still proceed. Excessive dosing is dangerous: residuals above roughly 0.02–0.05 mg/L entering fish tanks damage gills within hours, so contact chambers must be sized to consume the full dose, often followed by an activated carbon polisher or a degassing column and a UV destruct stage. Ozone also strips dissolved oxygen from the water column during decay, so aeration after contact is essential. Farms should log ORP continuously, calibrate probes weekly against standard solutions, and treat sudden ORP drops as a signal of rising organic load rather than probe failure. Correctly run, ozone improves water clarity, lowers biochemical oxygen demand, and sharply reduces pathogen pressure on fish.