I’ve walked into enough hatcheries to smell trouble before I even see the tanks. That distinct， earthy， stagnant odor of water that is “surviving” rather than thriving。
If you are running a commercial fishery or a high-end Recirculating Aquaculture System （RAS）， you know the constant battle： rising ammonia， stubborn nitrites， cloudiness， and the looming threat of a pathogen outbreak that could wipe out your entire stock in 48 hours。
For years， the industry relied on massive water changes or heavy antibiotic use. But regulations are tightening， and water is getting expensive。
There is a better way. It’s not magic， it’s chemistry. It’s Ozone。
However， I see too many facility managers hesitate because they’ve heard horror stories of ozone overdosing， or they simply don’t know how to size a system. This guide fixes that. I’m going to walk you through exactly how ozone works， how to implement it safely， and how to use it to drastically improve your Feed Conversion Ratio （FCR） and bottom line。
What Exactly is Ozone in Aquaculture？ （The Quick Definition）
Ozone （O3） is a highly reactive form of oxygen. In aquaculture， it serves as a powerful oxidizing agent that destroys organic waste， neutralizes ammonia and nitrite， and sterilizes water by killing bacteria， viruses， and fungi on contact. Unlike chemical treatments， it leaves no harmful residue—once it reacts， it simply turns back into pure oxygen， raising the Dissolved Oxygen （DO） levels in your tank。
Why Your Mechanical Filtration Isn’t Enough
Let’s get technical for a moment. You probably have drum filters， sand filters， and bio-filters. They are essential， but they have limits。
Mechanical filters remove solids. Bio-filters convert ammonia. But what about the Dissolved Organic Compounds （DOCs）？ These are the microscopic proteins， tannins， and fats from uneaten feed and fish waste that slip right through your mechanical filters。
When DOCs build up， three things happen：
1。 Water turns yellow/brown （tea-colored）。
2。 BOD （Biological Oxygen Demand） spikes， robbing your fish of oxygen。
3。 Bacteria thrive。 High DOC is an all-you-can-eat buffet for Aeromonas and other nasty pathogens。
This is where Ozone for Aquaculture changes the game. It acts as a “micro-flocculant。” It clumps these dissolved organics together so your mechanical filters can actually catch them。
The result？ Water so clear it looks like the fish are floating in air。
The ROI of Ozone： More Than Just Clear Water
I often have to justify the capital expenditure （CapEx） of an ozone system to CFOs. They see a cost； I see an investment. Here is the math I use：
1. Faster Growth Rates
Fish spend a lot of energy fighting off low-level infections and dealing with poor water quality. When you strip the water of pathogens and increase the ORP （Oxidation Reduction Potential）， fish stress drops. Energy previously used for immune response is redirected to growth。
2. Reduced Water Usage
In a RAS environment， water exchange is a major cost （pumping， heating， treating）. Because ozone prevents the buildup of non-biodegradable organics， you can recirculate the same water longer without quality degradation. I’ve seen facilities reduce daily water exchange by 30-40% after installing a proper ozone loop。
3. Disease Mitigation
Ozone kills bacteria， viruses， and parasites faster than chlorine and UV. It destroys the cell wall of the pathogen。
- Fact： UV usually only sterilizes the water passing through the light. Ozone provides a residual effect （if managed correctly） that cleans the plumbing lines， preventing biofilm buildup where pathogens hide。
Selecting the Right Equipment： CD vs. UV
If you take one thing away from this article， let it be this： Do not buy a UV-based ozone generator for commercial aquaculture。
UV Ozone Generators
These use ultraviolet light to split oxygen molecules。
- Pros： Cheap。
- Cons： Low output， low concentration （usually <1%）， bulbs degrade quickly， and they cannot produce enough pressure to inject properly into pressurized water lines。
Corona Discharge （CD） Generators
This is the industry standard. It uses a high-voltage electrical discharge to split oxygen。
- Pros： High concentration （6-12% by weight）， capable of high-pressure injection， durable， energy-efficient for the output。
- Verdict： For any tank over 1，000 gallons， Corona Discharge is the only serious option。
Critical Engineering： Injection and Contact Time
You cannot just bubble ozone into a tank with an airstone. That is dangerous and inefficient. Gas transfer is the hardest part of this equation。
The Venturi Injector
Based on my experience， the most reliable method is a Venturi injector. This device uses a pressure differential to suck the ozone gas into the water stream， creating a violent mix that dissolves the gas instantly。
The Contact Tank （Degassing Vessel）
This is where 90% of DIY setups fail. You need a dedicated vessel where the ozonated water sits for a specific period （Contact Time） before returning to the fish tank。
- Why？ You need time for the ozone to kill the pathogens （Reaction）。
- Why else？ You need to let the remaining ozone off-gas or decay so you don’t poison the fish。
Pro Tip： Always install an Ozone Destruct Unit on the air vent of your contact tank. Ozone gas is corrosive and harmful to human lungs. The destruct unit turns the off-gas back into safe oxygen。
Safety First： Understanding ORP and Toxicity
Ozone is a double-edged sword. Too little does nothing； too much kills your fish。
How do we control it？ We use ORP （Oxidation Reduction Potential）。
ORP measures the cleanliness of the water in millivolts （mV）. It is the speedometer for your ozone system。
ORP Target Ranges
| ORP Level (mV) | Water Condition | Action |
|---|---|---|
| < 200 mV | Poor quality, high organics | Increase Ozone |
| 250 – 300 mV | Sweet Spot for Aquaculture | Maintain |
| 350 – 400 mV | Sterile water (High clarity) | Monitor Closely |
| > 450 mV | DANGER ZONE | STOP Ozone |
The Danger of Bromates （Saltwater Warning）：
If you are running a marine/saltwater system， you must be extra careful. Ozone reacts with bromide in sea water to form bromine （which is toxic） and eventually bromate。
- My Rule： In saltwater， never exceed an ORP of 350mV. Ensure your protein skimmers are working perfectly， as activated carbon can help remove residual oxidants。
Sizing Your Generator： A Rule of Thumb
Calculating the exact ozone demand requires a lab analysis of your TOC （Total Organic Carbon） and COD （Chemical Oxygen Demand）. However， for estimation purposes， here is the formula I use for RAS systems：
10 to 15 mg of Ozone per 1 kg of Feed entering the system。
- Example： If you feed your fish 10kg of food per day。
- Calculation： 10kg * 15mg = 150mg/hr？ No。
- Ideally， you size based on the flow rate and the instantaneous demand。
Simplified Sizing Guide：
- Light Bio-load （Ornamental）： 2-3 grams of ozone per 1，000 gallons of water volume。
- Heavy Bio-load （Food Fish/Grow out）： 5-8 grams of ozone per 1，000 gallons （depending on feed rate）。
Note： Always buy a generator slightly larger than you think you need， and control it with a variable output dial or an ORP controller。
Maintenance： The Forgotten Factor
An ozone generator is not “set it and forget it。” Here is the maintenance schedule I recommend to my clients to ensure longevity：
1。 Check the Check Valve （Weekly）： Water backing up into the ozone generator is the #1 cause of failure. If the check valve fails， your expensive generator becomes a paperweight。
2。 Clean the Air Filter/Dryer （Monthly）： Ozone generators need dry， clean air. Humidity creates nitric acid inside the generator， which destroys the corona cell. Check your air dryer beads—if they are pink/wet， change them。
3。 Calibrate ORP Probes （Quarterly）： An uncalibrated probe is dangerous. If it reads 250mV but the water is actually 450mV， you will kill your fish. Clean and calibrate probes regularly。
FAQ： Common Questions About Ozone in Aquaculture
Q： Will ozone kill the beneficial bacteria in my bio-filter？
A： Only if you inject it directly into the bio-filter or overdose massively. If you inject ozone after the bio-filter and use a proper contact tank， the residual ozone should be gone before the water completes the loop back to the bio-filter. In fact， by reducing the organic load， ozone often makes bio-filters work more efficiently。
Q： Is ozone safe for shrimp/crustaceans？
A： Yes， but they are more sensitive than finfish. You must maintain a very stable ORP. Fluctuations stress shrimp during molting. Stick to the lower end of the ORP range （250mV）。
Q： Can I use oxygen concentrators with my ozone generator？
A： absolutely. In fact， I highly recommend it. Feeding an ozone generator with pure oxygen （90%+） instead of ambient air （21% oxygen） can double the ozone output and efficiency of the machine. It’s a vital upgrade for commercial operations。
Q： How quickly does ozone break down？
A： In water， the half-life of ozone is measured in minutes （usually 10-20 minutes depending on temperature and pH）， but in dirty water with high organics， it is consumed in seconds。
Conclusion： The Clear Choice
Deciding to use ozone for aquaculture is the transition point between a hobbyist mindset and a professional operation。
It gives you control. It takes the “luck” out of water quality and replaces it with engineering。
However， the hardware is only 50% of the solution. The integration—how you inject it， how you monitor it， and how you safeguard it—is where the success lies。
Don’t guess with your livestock。
If you are planning a new facility or retrofitting an existing RAS and need help sizing the right ozone generator and injection skid， we can help。
【Click here to contact our Engineering Team for a Free Sizing Consultation】 – Let’s get your water crystal clear and your fish growing faster。