How Ozone Works
Ozone oxidises the cell membranes of pathogens and the organic matrix of biofilms. At a contact dose of 2–5 minutes, it achieves 99.9%+ destruction of most hydroponic pathogens, including Pythium and Phytophthora.
It penetrates biofilms more effectively than UV-C or chemical disinfectants.
Residual Ozone: A Critical Hazard
Above 0.05 mg/L — oxidative stress to roots; above 0.1 mg/L — direct root damage.
Safe residual ozone concentration for irrigation: <0.02 mg/L. Testing: colorimetric test kits (DPD or indigo methods).
Degassing: Methods for Removing Residual Ozone
Natural decomposition: hold in a reservoir. At 20°C and pH 7.0 — half-life 15–20 minutes; at pH 6.0 — 30–60 minutes.
Air stripping: purges ozone within 5–10 minutes but requires ventilation to remove off-gassed ozone safely.
Activated carbon: catalytically destroys ozone without releasing it into the air.
Operator Safety
O₃ is toxic at just 0.1 ppm (OSHA limit: 0.05 ppm). Olfactory adaptation occurs rapidly — smell is not a reliable indicator of safe levels.
Requirements: generation only in an isolated or well-ventilated space, an ozone detector in the room, PPE when working with the generator.
Three Mistakes That Cost the Most
- Irrigating without degassing — 10 minutes of contact at 0.05–0.1 mg/L causes chemical root stress
- Assessing residual ozone by smell — olfactory adaptation makes this unreliable; only a test kit is a valid method
- Running a generator without an ozone detector — a leak goes undetected until poisoning symptoms appear
Signs of a Correct Setup
- Residual ozone after degassing <0.05 mg/L
- Roots are white or cream-coloured with no signs of chemical burn
- Solution ORP 650–750 mV