Industry Solutions
How to Size Oxygen Supply for RAS: Biomass, Feed, DO, Peak Demand and Oxygen Generator Capacity
Size RAS oxygen supply from biomass, feed, temperature, DO and peak demand - not tank volume alone. Include fish and biofilter oxygen demand.
RAS oxygen demand changes with production.
The selection question is:
What oxygen mass must be transferred during the highest realistic demand period?
Start With Biomass and Feed
Collect fish species, current biomass, target biomass, daily feed, peak feeding rate, feeding schedule and water temperature.
Feed and biomass are stronger design inputs than tank volume alone.
1. Measure Current DO
Record DO at fish tank inlet/outlet, biofilter inlet/outlet and peak feeding periods.
A single daytime reading may miss the real minimum.
2. Define the Operating DO Target
Required DO depends on species, life stage, temperature, stocking density and system design.
Do not use one universal target for every RAS.
3. Include Biofilter Oxygen Demand
Nitrifying bacteria consume oxygen too.
The oxygen system should support both fish and biological filtration.
A fish tank can appear acceptable while the biofilter remains oxygen-limited.
4. Check Temperature
Warm water holds less dissolved oxygen while fish metabolism can increase.
Include normal, maximum and seasonal temperature.
5. Review Peak Demand After Feeding
Fish respiration rises after feeding.
The feeding schedule therefore matters, not only the total daily ration.
6. Separate Oxygen Production From Oxygen Transfer
An oxygen generator produces gas.
Possible contact methods include oxygen cones, low-head oxygenators, pressurized contactors or gas-liquid mixing devices.
Generator and contactor capacity should be checked together.
7. Account for Transfer Efficiency
Not all generated oxygen dissolves into the water.
Actual transfer depends on contactor design, pressure, water flow, gas flow, inlet DO, temperature, salinity and off-gas.
Do not equate gas production with oxygen delivered to fish.
8. Check Redundancy
Review standby oxygen generation, emergency oxygen, backup power, alarms and automatic changeover.
The appropriate backup strategy depends on fish value and acceptable response time.
9. Check Gas Quality and Pressure
Confirm oxygen purity, flow, delivery pressure and contactor requirements.
The generator must match the downstream gas-transfer equipment.
10. Include Future Biomass
A system sized for current stocking may become undersized near harvest.
Use planned maximum biomass and feed rate.
Practical RAS Oxygen Checklist
Data Group | Information | Purpose |
|---|---|---|
Fish | Species and biomass | Respiration load |
Feed | Daily and peak | Demand indicator |
Temperature | Normal and maximum | DO capacity |
DO | Inlet, outlet, minimum | Current condition |
Biofilter | Ammonia load and flow | Nitrification duty |
Recirculation | Flow rate | Contactor duty |
Oxygen Source | Purity, pressure, kg/h | Gas supply |
Contactor | Type and performance | Transfer |
Backup | Emergency oxygen/power | Reliability |
Common Oxygen-Sizing Mistakes
Sizing From Tank Volume
Biomass and feed are more important.
Ignoring Biofilter Demand
Nitrification consumes oxygen too.
Using Average Demand Only
Peak feeding and warm-water conditions matter.
Confusing Gas Production With Transfer
Oxygen must actually dissolve into the water.
Ignoring Backup
Oxygen failure can become an immediate production risk.
Technical Basis
SRAC RAS guidance emphasizes that fish and biofilter microorganisms both require oxygen and that demand increases as fish biomass and feeding approach maximum production.
The practical rule is:
size oxygen supply from peak biological demand, then verify gas transfer and emergency backup.
Need Help Reviewing RAS Oxygen Supply?
Send HydroNovus the fish species, biomass, feed rate, temperature, current/target DO, recirculation flow, biofilter load, existing oxygen equipment and backup arrangement.
HydroNovus can provide a preliminary oxygen-supply review covering generator and contactor duty.