RAS Oxygen & Biofilter Sizing

Aquaculture, feed conversion and RAS calculators

From recirculating systems to ponds, Tenselo sizes oxygen demand, biofilters, aeration and water exchange so your fish thrive and feed isn't wasted. Built for aquaculture engineers and farm managers.

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Aquaculture & RAS in Tenselo

A short introduction to what Tenselo covers in this category.

Video summary: Fish stocking, oxygen demand, biofilter sizing, water exchange, pumping duty and supporting recirculating-aquaculture-system hydraulics.

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A worked example

Barramundi RAS oxygen demand

AQR-021 · fish plus biofilter demand

These figures were verified in the live AQR-021 calculator. Every result Tenselo produces shows the inputs it used and the method behind it, so the work can be checked rather than taken on trust.

Inputs

Stock biomass 1,500 kg

Feed rate 18 kg/day

Water temp 26 °C

Species Barramundi

Results

19.3 kg/d

Fish oxygen

4.1 kg/d

Biofilter oxygen

23.4 kg/d

Total oxygen

1.27 kg/h

Peak oxygen

8.1 mg/L

DO saturation

6.0 mg/L

Minimum DO

Why it matters on the job

Assess oxygen and ammonia loads

Estimate oxygen and ammonia loads from biomass, feed rate and the entered operating assumptions.

Assess biofilter media requirements

Estimate MBBR or fixed-film media requirements from nitrogen load and the selected treatment assumptions.

Review water exchange

Assess make-up and exchange requirements alongside water quality, flow and pumping duty.

Aquaculture and RAS design calculators

Tenselo provides aquaculture and recirculating aquaculture system (RAS) calculators for feed conversion, fish biomass, stocking density, oxygen demand, biofilter sizing and water exchange. Start with the species, working water volume and production conditions, then assess the relevant treatment and hydraulic duties.

Feed conversion ratio calculator

AQR-002, FCR & Feed Cost, uses starting biomass, final biomass and feed used to calculate economic feed conversion ratio and feed cost per kilogram of biomass gain. An optional mortality weight supports a separate biological FCR calculation. Keep the recording period and biomass accounting consistent.

Static worked example: starting biomass of 200 kg, final biomass of 1,200 kg and 1,100 kg of feed give a biomass gain of 1,000 kg. Economic FCR = 1,100 / 1,000 = 1.10. At a feed price of $2.20/kg, the feed cost is $2.42 per kilogram of gain. This example covers feed cost only; labour, energy, treatment and other production costs are additional.

Fish stocking density and biomass calculator

AQR-007, Fish Stocking Density & Biomass, calculates biomass and density from fish count, average weight and working water volume. It compares the result with the entered target, maximum density and safety margin. The chosen density limits are design inputs, so a numerical result alone does not demonstrate that a species or system can sustain the proposed stock.

Use the feed-rate calculator and feed protein to total ammonia nitrogen (TAN) load calculation to describe the load that the life-support equipment must handle. Check the production period, temperature and feed assumptions across the calculations.

RAS oxygen demand and aeration sizing

AQR-021, Oxygen Demand - Fish + Biofilter, considers biomass, species, water temperature, feed and nitrification load, with an entered peak allowance and dissolved-oxygen target. Review fish demand and biofilter demand together, then investigate aeration diffuser sizing, oxygen cone or low-head oxygenation sizing and emergency oxygen backup for the relevant system. See the verified AQR-021 example.

Aquaculture biofilter sizing

AQR-012, Moving Bed Biofilter Sizing, assesses media surface area, media volume and tank volume from TAN load, temperature, the selected media, an entered removal rate, fill percentage and safety factor. Confirm the media data and removal rate for aquaculture conditions with the supplier. A rate used for wastewater treatment is not automatically suitable for a low-TAN RAS duty.

Related tools cover trickling or fixed-bed biofilters, nitrate build-up and water exchange, nitrification alkalinity consumption and drum filter sizing. Hydraulic flow, solids removal and water quality need to be assessed alongside the biological treatment.

New accounts require approval. These are public tool descriptions and a static worked example; running project calculations requires authorised application access. See availability and registration. Review the complete production and life-support design with an aquaculture specialist, using suitable species and supplier data.

AQR-021 · live calculation example

RAS oxygen demand for 1,500 kg of barramundi

How much oxygen-transfer capacity should a preliminary RAS design allow for when 1,500 kg of barramundi receive 18 kg of feed per day at 26 °C? This hypothetical example separates fish demand, biofilter nitrification demand and the peak allowance.

Life-support questionWhat continuous and peak oxygen duties must the next design stage carry?

Fish and feeding1,500 kg at 26 °CBarramundi · 18 kg feed per day

Continuous oxygen balance19.3 + 4.1 = 23.4 kg/dayFish demand plus biofilter demand

Preliminary peak duty1.27 kg O₂/h30.4 kg/day equivalent

Fish oxygen19.3 kg/dlarger of the metabolic and feed-based checks

Biofilter oxygen4.1 kg/d0.9 kg TAN/day × 4.57 kg O₂/kg TAN

Total continuous23.4 kg/dequivalent to 0.98 kg O₂/h

Peak oxygen duty1.27 kg/h30% allowance applied to the continuous total

Calculated preliminary peak duty: 1.27 kg O₂/h. AQR-021 reports 23.4 kg/day of continuous demand and 30.4 kg/day at the entered peak factor. Use that peak result to develop oxygen-cone, low-head oxygenation, diffuser and emergency-backup checks.

Verified live inputs

Feed oxygen factor: 0.25 kg O₂/kg feed
TAN nitrified: 0.9 kg/day
Peak allowance: 30%
Minimum DO target: 6.0 mg/L

This static hypothetical example was verified in the live Tenselo AQR-021 calculator on 16 September 2026. Aquaculture systems can fail rapidly and harm stock, so use a competent aquaculture professional and current supplier and husbandry data. Calculator execution and project PDF reports require authorised application access.

Method & worked example

Calculate feed conversion ratio over a defined period

Feed conversion ratio (FCR) compares feed used with biomass gain over the same period. State both measurement bases before comparing batches.

Illustrative closed cohort: no stocking, harvests or mortality during the period
Measurement	Value
Starting biomass	1,000 kg
Ending biomass	1,200 kg
Biomass gain	1,200 − 1,000 = 200 kg
Feed supplied	240 kg
Apparent FCR	240 / 200 = 1.20 kg feed per kg gain

Keep the stock account consistent

Transfers, harvests and mortality change the biomass balance. Record them and define how they are included before calculating or comparing FCR. State whether the numerator is feed supplied or estimated feed consumed; these are different measures.

FCR is a performance measure, not a feeding recommendation. A biofilter or oxygen system also needs peak daily feed, species and size, water temperature, water quality, process performance and an appropriate design basis. An annual average FCR does not establish peak treatment load.

Browse the aquaculture calculator catalogue for feed, biomass, oxygen and biofilter tasks. Connect those loads to water treatment and circulation pumping.

Reference: FAO guidance on feeding and feed conversion. The numbers here are an illustrative calculation, not a species benchmark.

Static educational example · Updated 1 October 2026 · Methods and limitations. Project calculations run in the subscription application; New accounts require approval.

What is in this category

53 Aquaculture calculators

Every calculator in this category, by its reference code. Running them requires an approved Tenselo account with access to the relevant calculators.

AQR-001 Biofloc Carbon Dose

Carbohydrate addition to control ammonia heterotrophically in biofloc systems (C:N basis)
AQR-002 FCR & Feed Cost

Feed conversion ratio, feed cost per kg gain and gross value
AQR-003 Feed Protein to TAN Load

Ammonia (TAN) production from feed - the master input for biofilter sizing
AQR-004 Feed Rate & Daily Feed Load

Daily/weekly/monthly feed, cost and the TAN-driving feed load
AQR-005 Fish Grading Split

Counts, biomass and tanks per size grade within density limits
AQR-006 Fish Growth & Harvest Forecast

Days to harvest, harvest date and biomass from SGR
AQR-007 Fish Stocking Density & Biomass

Current vs maximum biomass and stocking density, with spare capacity
AQR-008 Nitrate Build-up & Water Exchange

Nitrate rise and the water exchange needed to stay below a target
AQR-009 Nitrification Alkalinity Consumption

Alkalinity used by nitrification and the buffer chemical needed to hold it
AQR-010 Nitrite Toxicity & Chloride Protection

Chloride:nitrite ratio check and the salt dose to protect fish
AQR-011 Un-ionised Ammonia (NH3) Toxicity

Toxic NH3 fraction from TAN, pH, temperature & salinity (Emerson 1975)
AQR-012 Biofilter Sizing - Moving Bed (MBBR)

Media volume & tank size for a moving-bed nitrifying biofilter
AQR-013 Biofilter Sizing - Trickling / Fixed Bed

Media area, volume, plan area and footprint for a fixed-media biofilter
AQR-014 Carrying Capacity by Biofilter

Maximum feed and biomass your biofilter can support
AQR-015 Carrying Capacity by Hydraulic Flow

Maximum biomass from flow-per-kg and tank turnover limits
AQR-016 Carrying Capacity by Oxygen

Maximum fish biomass your oxygen system can support
AQR-017 Aeration Diffuser Grid Sizing

Air flow, diffuser count and blower pressure for diffused aeration
AQR-018 CO2 Production & Degassing

CO2 made by the system and the air flow / degasser to strip it out
AQR-019 Emergency Oxygen Backup

Oxygen storage to keep fish alive through a pump/power/aeration failure
AQR-020 Oxygen Cone / LHO Sizing

Oxygen gas flow and transfer check for a cone or low-head oxygenator
AQR-021 Oxygen Demand - Fish + Biofilter

Total O2 demand from fish, feed and nitrification (peak & required transfer)
AQR-022 Oxygen Supersaturation / Gas Bubble Disease

DO % saturation, total gas pressure and GBD risk
AQR-023 Aquaculture Sludge Dewatering

Dry solids, wet sludge, dewatered cake and polymer from feed
AQR-024 Drum Filter Sizing

Screen area, solids capture and backwash water for a microscreen drum filter
AQR-025 Foam Fractionator / Protein Skimmer

Skimmer flow, contact volume and air for foam fractionation
AQR-026 Ozone Dose for Aquaculture

Ozone generator size, contact tank and bromate/off-gas safety for RAS
AQR-027 Settling Cone / Radial Flow Settler

Surface area, vessel diameter and retention for settleable-solids removal
AQR-028 UV Dose for Aquaculture

Delivered UV dose after UVT, fouling and lamp ageing vs the target
AQR-029 Circular Tank Inlet Hydraulics

Inlet jet velocity, indicative rotational velocity and solids sweep
AQR-030 Intake Screen Approach Velocity

Fish-safe screen area from intake flow and approach-velocity limit
AQR-031 Make-up Water Requirement

Daily make-up and discharge from exchange, backwash, purge & evaporation
AQR-032 RAS Mass Balance Summary

One-page design summary - loads, sizes and the limiting bottleneck
AQR-033 RAS Tank Turnover Flow

Recirculation flow, residence time and pump arrangement
AQR-034 Salinity / Salt Addition

Salt to raise salinity or chloride, with a species-limit check
AQR-035 Temperature Heating / Chilling Load

Heat-up energy, hold load and running cost for a heater/chiller/heat-pump
AQR-036 Fry / Fingerling Tank Sizing

Tank volume, count, flow and feed for a nursery batch
AQR-037 Hatchery Egg Incubator Flow

Flow, oxygen and unit count for egg jars / trays / troughs
AQR-038 Hatchery Incubation Degree-Days

Hatch date forecast from accumulated temperature (degree-days)
AQR-039 Pond Aeration Sizing

Aerator power & count for ponds, with night low-DO risk
AQR-040 Pond Turnover / Circulation Pumping

Flow, pump duty, power and running cost for pond circulation/exchange
AQR-041 Predator / Bird Netting Load

Support-cable load, sag and tension for pond/tank bird netting (indicative)
AQR-042 Raceway Flow & Velocity

Velocity, residence time, turnover and solids transport for a raceway
AQR-043 Fish Acclimation / Salinity Change Rate

Safe acclimation time and drip/exchange flow for temp & salinity change
AQR-044 Fish Transport Tank Oxygen

Oxygen, loading and DO check for live-fish transport
AQR-045 Harvest Ice Requirement

Ice to chill and hold harvested fish, with ice:fish ratio
AQR-046 Live Fish Transport CO2 Build-up

CO2 produced and final concentration in a transport tank
AQR-047 Processing Wash Water Demand

Wash water, peak flow and wastewater volume for fish processing
AQR-048 Purge / Depuration Tank Sizing

Tank volume, flow and oxygen for holding/purging before harvest
AQR-049 Aquaculture Water Analysis Interpreter

Full water test -> per-parameter status, NH3/nitrite/CO2 risk and treatment actions
AQR-050 Biosecurity Footbath / Dip Dose

Disinfectant product per footbath / equipment dip, with refresh schedule
AQR-051 Mortality Event Response

Oxygen, ammonia and water-exchange response after a die-off
AQR-052 Quarantine System Sizing

Tank, flow, feed, ammonia, oxygen and biofilter for a quarantine batch
AQR-053 RAS Alarm & Backup Capacity Check

Time-to-unsafe-DO vs backup & response - protected / vulnerable / critical

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