Clearer water in dense systems.
Ozone oxidises dissolved organics and colour that filters cannot catch. Paired with a protein skimmer, it lifts removal further. Below: how much to dose, how to control it, and how to keep fish and people safe.
usually through a skimmer
sets the dose
controls it
destroyed, room ventilated
Oxidises what filters leave behind.
Ozone is a strong oxidiser. In a RAS it breaks down dissolved organics and colour, helps fine particles clump so a skimmer or filter can remove them, and kills bacteria it contacts. The same strength makes it harmful to fish, to the biofilter and to people if it reaches them.
- water colour, UV transmittance and skimmer performanceImproves:
- the fish tanks or the biofilter. It is dosed into a side stream and given time to react.Must not reach:
- a replacement for solids removal or a biofilterIs not:
Dose follows feed.
Organics come from feed, so ozone dose is usually expressed in grams of ozone per kg of feed per day. Published figures show where the useful range ends.
Upper limit for black porgy, based on gill and liver damage
20 g O₃ per kg feed per day
Dose used to disinfect water ahead of UV, held by ORP control
About 29 g O₃ per kg feed
The last figure is for full disinfection with UV after it, not routine water quality. Higher dose means more risk of residual ozone, so it needs tighter control.
A worked example
A farm feeding 500 kg a day at 15 g per kg needs about 7.5 kg of ozone a day, or roughly 310 g an hour. The generator is then sized above that, so the controller can turn it down. Illustrative figures, not a quote.
ORP sets the dose, not a fixed number.
Ozone demand changes with feed and water. Most systems control it with an ORP (oxidation-reduction potential) probe that turns ozone output up or down. A salmon RAS study ran loop treatment at 300–350 mV (). In the USDA study, ORP was held at 450–525 mV, measured at the contact chamber outlet before UV, not in the tanks ().Scientific Reports, 2026USDA ARS
ORP probe in the right place
Reading where ozone has reacted tells you what reaches the fish
High-ORP cut-out
Stops ozone if ORP rises above a safe limit
Probe cleaning and calibration
ORP probes drift; a drifting probe doses wrongly
Dose turned up slowly at start-up
The system’s ozone demand is found by measuring, not guessing
Ozone harms people as well as fish.
Residual ozone reaching the tanks
Side-stream dosing, reaction time, ORP control and a high-ORP cut-out
Ozone gas in the room
Off-gas from the skimmer or contact chamber goes to an ozone destructor; the room is ventilated
Leaks at the generator or pipework
Ozone-resistant materials; an ambient ozone monitor and alarm in the plant room
Seawater by-products
In seawater, ozone reacts with bromide to form oxidants that last longer than ozone itself, and bromate. Marine systems dose more carefully and check residual oxidant before water returns.
When something looks wrong.
Fish gasping, flared gills, after a dose change
Residual oxidant reaching the tanks
ORP; stop ozone and check the controller and cut-out
ORP not rising
Generator output low, wet feed gas, or very high organic load
Generator; feed gas dryness; feed load
ORP reading jumps or drifts
Fouled or uncalibrated probe
Clean and calibrate
Ozone smell in the room
Leak, or off-gas not destroyed
Ambient monitor; destructor; joints
Skimmer foam falls
Dose or skimmer air changed
Ozone output; skimmer air and water level
Ozone sized with the skimmer and controls.
Ozone is only safe as part of a designed side stream. We size the generator, skimmer, controls and room together.
Sized on feed
Dose in g per kg of feed, with the calculation sent to you.
Dose control designed in
ORP control and a high-ORP cut-out are part of the design.
Room planned
Ventilation and off-gas handling planned in the layout.
Fitted and tested
Supplied, fitted and tested with the rest of the system before it ships.
When dosed in a side stream, given time to react and controlled by ORP before the water returns, yes. Ozone reaching the tanks damages gills, which is why dose control is part of the design.
It is the usual pairing. The skimmer gives ozone contact time, removes what it breaks down, and collects the off-gas.
It follows feed. Published studies point to about 15–20 g of ozone per kg of feed for routine use. We size the generator above your dose so the controller can turn it down.
It depends on where the probe sits and your system. Studies report 300–350 mV for loop treatment; readings at a contact chamber outlet run higher. Your engineer sets the target and the cut-out.
Yes, with care. In seawater ozone forms bromine oxidants and bromate, which last longer than ozone. Dose is lower and residual oxidant is checked before water returns.
Oxygen gives more ozone from the same generator. If the farm has PSA oxygen, it can often supply the ozone generator as well.
It can, if residual oxidant reaches it. Dosing in a side stream and controlling ORP keeps it away from the media.
Ventilation, an ambient ozone monitor, and off-gas going to a destructor rather than into the room.
Send your system. We size ozone and the skimmer together.
Peak daily feed, salinity and flow. We return the ozone dose, generator size, skimmer and controls.
- Dose sized on feed
- ORP control and cut-out
- Room and off-gas planned
- Fitted and tested with the system