What does ozone do in a recirculating aquaculture system?

In a recirculating aquaculture system (RAS), ozone is used to inactivate pathogens (bacteria, viruses, fungal spores), oxidise dissolved organic matter that filtration cannot catch, break up fine solids so they coagulate and can be removed, and polish water clarity. The net result is healthier stock, better feed conversion and lower system fouling.

Does ozone improve water clarity in RAS?

Yes. Ozone oxidises the colloidal organic compounds and dissolved colour bodies that turn RAS water yellow over time. Combined with foam fractionation / protein skimming it visibly improves clarity, which also makes UV polishing (if fitted) more effective.

Can ozone reduce pathogens in aquaculture water?

Yes — that is one of its primary roles in RAS and hatcheries. Ozone is effective against a wide range of fish and shellfish pathogens. Dose is matched to the specific application and operating ORP, with the ozone-destruct and degassing stages designed to ensure no residual reaches the fish tanks.

What are the risks of overdosing ozone in fish systems?

Excess dissolved ozone is harmful to fish. Aquaculture ozone systems are therefore designed conservatively: dose is controlled by ORP (or dissolved-ozone) feedback, residual ozone is destroyed in a degassing / off-gas stage before water returns to the tanks, and automatic shut-down responds to high-ORP or high-ambient-ozone alarms. Dosing, monitoring and shut-down should always be designed and commissioned together — talk to us at /contact.

How is ORP used to control ozone dosing?

Oxidation-reduction potential (ORP), measured in millivolts, is the standard real-time indicator of how much oxidising power is present in the water. Aquaculture systems set an ORP set-point in the loop (commonly somewhere in the 280–350 mV range for marine RAS, lower for freshwater) and the controller modulates ozone output to hold the set-point. The exact set-point depends on species, life-stage and water chemistry.

Does ozone work with protein skimmers or foam fractionation?

Yes — ozone and foam fractionation are a very effective pairing in RAS. Ozone is typically injected at the foot of the skimmer; the bubbles provide both gas-liquid mass transfer for the ozone and the rising contact column for foam fractionation. The foam carries oxidised organics out of the loop and any residual ozone leaves with the off-gas, which is then destroyed.

Ozone Technologies Ltd

Aquaculture Ozone Treatment

Name: Ozone Technologies Ltd
Address: 22B Turner Place, Onekawa, Napier, Hawke's Bay, 4110, NZ
Telephone: +64 6 8432881
Price range: $$$$

Ozone water treatment for RAS, hatcheries and commercial aquaculture

Aquaculture is one of the fastest-growing food sectors globally, and one of the most demanding water-treatment applications. Fish, shellfish and crustacean health is directly determined by water quality — dissolved oxygen, ammonia, nitrite, organic load, pathogens and fine solids all need active management. In recirculating aquaculture systems (RAS), where 95–99% of water is reused, water-treatment failure means stock loss. Ozone is the single most powerful tool the aquaculturist has: it kills pathogens, oxidises organic load, breaks up fine solids for filtration, and improves water clarity — all without leaving any residue in the water that contacts the fish.

How ozone works in aquaculture

Ozone delivers four distinct benefits in aquaculture water. First, pathogen inactivation: at properly-controlled doses, ozone destroys viruses (including IHNV, VHSV and Nodavirus), bacteria (Vibrio, Aeromonas, Yersinia, Renibacterium) and parasites (sea lice, amoebic gill disease) that would otherwise circulate endlessly through a RAS. Second, organic oxidation: dissolved organic carbon (DOC) from fish waste and feed is broken down into smaller, more biodegradable molecules that the biofilter can process — preventing the brown 'tea-coloured' water typical of un-ozonated RAS. Third, micro-flocculation: ozone causes fine particles to aggregate, allowing them to be removed by drum filters and protein skimmers that would otherwise miss them. Fourth, taste improvement (for harvested fish): ozonated water removes geosmin and MIB that cause off-flavours in farmed fish.

RAS (Recirculating Aquaculture Systems)

RAS systems demand the highest level of water-treatment integration in aquaculture. A typical RAS treatment loop includes drum or belt filtration for solids removal; a biofilter (typically moving-bed or fluidised-bed) to convert ammonia to nitrate; degassing for CO₂ removal and O₂ supplementation; ozone treatment for pathogen control and DOC oxidation; a residual ozone reaction tank; quenching (typically with sodium thiosulphate or GAC) to remove residual ozone before the water re-contacts fish; and pH and temperature control. Our role is to design and supply the ozone module of this loop, integrated with the biofilter and degasser controls. Get the dose right and the RAS thrives. Get it wrong and you damage gills or kill the biofilter — both of which we are constantly engaged to help operators recover from after they've bought cheap ozone equipment elsewhere.

Hatcheries and quarantine systems

Hatchery water must be effectively pathogen-free. Egg and larval stages are extraordinarily vulnerable to bacterial and viral infection, and a single pathogen breakthrough can destroy a season's production. We supply ozone-based hatchery water treatment for finfish, shellfish and crustacean hatcheries, with residual-ozone quenching tuned for the sensitivities of larval life stages. Quarantine facilities — used to hold and treat incoming broodstock or imports before they enter the main system — use ozone as the primary disinfection barrier, often in combination with UV, to ensure the main population is never exposed to imported disease. Our protein skimmers (IPS series) are widely used in marine hatcheries to remove the organic load that ozone helps create.

Marine aquariums and public aquaria

Public aquariums face the same water-treatment challenges as commercial aquaculture, plus the additional requirement that the water must be crystal clear for visitor experience. Ozone is the foundation of marine aquarium life support, removing the organic load that causes yellowing and turbidity while disinfecting recirculating seawater. Our work in this segment includes Reef HQ and a range of other aquatic display facilities. The IPS protein skimmer range is specifically engineered for ozone-injection in marine recirculating systems, with corrosion-resistant materials throughout and standard sizes treating water flows from 10 to 100 m³/h. Salt-water aquaria require ozone-compatible materials throughout — we don't cut corners on this and have systems running for 15+ years in continuous marine service.

Safety: residual ozone and fish welfare

Ozone is highly toxic to fish at concentrations well below those used for water treatment. Residual ozone reaching fish tanks at >0.01 mg/L can damage gills; at >0.05 mg/L it is acutely lethal. This is why ozone treatment in aquaculture MUST be designed with a properly-sized reaction tank (typically 15–30 minutes contact time) followed by an active quenching stage and online residual-ozone monitoring with hard-wired interlock that halts ozone dosing on any residual breakthrough. Cheap aquaculture ozone systems frequently lack proper quenching or monitoring — when something goes wrong, the operator only finds out when stock is dying. Every system we design includes redundant residual-ozone monitors, automatic dose shutoff, and an emergency quenching reservoir.

Key benefits

What you can expect from a Aquaculture Ozone Treatment project with Ozone Technologies.

Pathogen control: viruses, bacteria, parasites and amoebae
DOC oxidation: clear water in continuous RAS operation
Micro-flocculation: improves drum-filter and skimmer performance
Off-flavour removal: geosmin and MIB control for harvest quality
Integrated with biofilter, degasser and skimmer designs
IPS protein skimmer range for marine recirculating systems
Hatchery-grade quenching for larval life stages
Redundant residual-O₃ monitoring with hard-wired interlocks
References: Huon Salmon (Tasmania), NIWA, Reef HQ, United Fisheries
Material selection for continuous marine / salt-water service

Quick answers

Common questions

What does ozone do in a recirculating aquaculture system?: In a recirculating aquaculture system (RAS), ozone is used to inactivate pathogens (bacteria, viruses, fungal spores), oxidise dissolved organic matter that filtration cannot catch, break up fine solids so they coagulate and can be removed, and polish water clarity. The net result is healthier stock, better feed conversion and lower system fouling.
Does ozone improve water clarity in RAS?: Yes. Ozone oxidises the colloidal organic compounds and dissolved colour bodies that turn RAS water yellow over time. Combined with foam fractionation / protein skimming it visibly improves clarity, which also makes UV polishing (if fitted) more effective.
Can ozone reduce pathogens in aquaculture water?: Yes — that is one of its primary roles in RAS and hatcheries. Ozone is effective against a wide range of fish and shellfish pathogens. Dose is matched to the specific application and operating ORP, with the ozone-destruct and degassing stages designed to ensure no residual reaches the fish tanks.
What are the risks of overdosing ozone in fish systems?: Excess dissolved ozone is harmful to fish. Aquaculture ozone systems are therefore designed conservatively: dose is controlled by ORP (or dissolved-ozone) feedback, residual ozone is destroyed in a degassing / off-gas stage before water returns to the tanks, and automatic shut-down responds to high-ORP or high-ambient-ozone alarms. Dosing, monitoring and shut-down should always be designed and commissioned together — talk to us at /contact.
How is ORP used to control ozone dosing?: Oxidation-reduction potential (ORP), measured in millivolts, is the standard real-time indicator of how much oxidising power is present in the water. Aquaculture systems set an ORP set-point in the loop (commonly somewhere in the 280–350 mV range for marine RAS, lower for freshwater) and the controller modulates ozone output to hold the set-point. The exact set-point depends on species, life-stage and water chemistry.
Does ozone work with protein skimmers or foam fractionation?: Yes — ozone and foam fractionation are a very effective pairing in RAS. Ozone is typically injected at the foot of the skimmer; the bubbles provide both gas-liquid mass transfer for the ozone and the rising contact column for foam fractionation. The foam carries oxidised organics out of the loop and any residual ozone leaves with the off-gas, which is then destroyed.

More background: case studies · about Ozone Technologies · contact an engineer.

Get expert advice on your aquaculture ozone treatment project

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+64 6 8432881 info@ozonenz.comNapier, New Zealand