Biofloc C:N Calculator Pro v3.0

🎯Production Stage Preset

Standard juvenile grow-out: target C:N 12-15, normal feed rate.

🌊Pond & Water Parameters

Pond Volume

m³

Salinity

ppt

Temp

°C

mg/L

TAN

mg/L

NO₂⁻-N

mg/L

Alkalinity

mg/L

🦐Shrimp Stocking

Density

/m³

Avg Weight

Survival

📦

Estimated standing biomass 1.7 tonnes · feeding rate 2.4% of biomass

🍤Feed Input

Daily Feed

kg/day

Protein

Feed C:N ratio

N excretion

⚙️Carbon Strategy

Target C:N Ratio

Carbon Source

Source price

/kg

Currency

Target Alkalinity

mg/L

Liming Agent

Imhoff Cone

mL/L

Aerator capacity

kg O₂/h

System Status

LOW RISK

TANSAFE NH₃SAFE NO₂SAFE DOOK

Today's Carbon Dose

kg of Sucrose

≈ $0.00 daily cost · 0 g/m³

⏱️ Application Schedule

No supplemental carbon needed.

⚖️C:N Ratio Dial

🔍What Your Results Mean

📊 System Risk Assessment

Your system is currently operating within safe parameters. The calculated carbon dose will maintain heterotrophic bacterial dominance, keeping TAN and NH₃ at manageable levels through bacterial assimilation.

✅ Recommended Actions

Continue regular monitoring of TAN, NH₃, and NO₂ every 12-24 hours
Maintain current C:N ratio and carbon dosing schedule
Monitor dissolved oxygen before and after carbon application

References: Avnimelech (2009); Ebeling et al. (2006); Hargreaves (2013)

⚛️Nitrogen Budget

N load from feed 0 g/day

TAN excreted to water 0 g/day

C from feed (heterotroph-available) 0 g/day

Total C needed (substrate basis) 0 g/day

Supplemental C required (maintenance) 0 g/day

Correction C for excess TAN 0 g (one-time)

Total C to dose today 0 g total today

N assimilated by bacteria (target) 0 g/day

Predicted residual TAN 0 g/day

⚛️ Understanding Your Nitrogen Budget

The nitrogen budget shows how feed protein converts to ammonia and how carbon dosing drives bacterial assimilation. When supplemental carbon matches or exceeds the C:N target (typically 12-20:1), heterotrophic bacteria convert toxic ammonia into microbial biomass (biofloc), which shrimp can consume as a protein-rich food source.

🎯 How to Optimize Nitrogen Management

High TAN (>2 mg/L): Increase C:N ratio to 18-20:1 temporarily. Add carbon in 3-4 splits over 12 hours. Reduce feeding by 20-30% until TAN drops below 1.5 mg/L (Avnimelech, 2009; Crab et al., 2012)
High residual N predicted: If residual TAN >200 g/day, raise target C:N to 18:1 or switch to lower-protein feed (28-32%). Consider adding nitrifying bacteria inoculum to establish autotrophic pathway (Ebeling et al., 2006)
Feed C sufficient: When feed waste alone meets C:N target, skip dosing but verify TAN at next test. This typically occurs with low-protein feeds (<30%) or low feeding rates (<2% biomass) (Hargreaves, 2013)
Correction dosing: For accumulated TAN >1 mg/L, apply correction dose in first split, then maintenance. Monitor TAN every 4 hours during correction period

References: Avnimelech (1999, 2009); Ebeling et al. (2006); Crab et al. (2012); Hargreaves (2013)

☠️Toxicity Analysis

Un-ionised NH₃-N (toxic form) 0.00 mg/L

% of TAN as NH₃ 0%

pKa at T, S 9.18

NH₃ safety margin (chronic) 0 ×

☠️ Understanding Ammonia Toxicity

Total Ammonia Nitrogen (TAN) exists as two forms: ionized ammonium (NH₄⁺) and un-ionized ammonia (NH₃). Only NH₃ is toxic to shrimp gills and hemolymph. The proportion of NH₃ increases dramatically with pH and temperature — at pH 8.0 and 28°C, approximately 3-5% of TAN is toxic NH₃. Even low TAN can become lethal if pH rises above 8.5.

🛡️ How to Manage Ammonia Toxicity

NH₃ >0.15 mg/L (CRITICAL): Stop feeding immediately. Lower pH gently with CO₂ injection or acid drip (food-grade phosphoric acid at 1:1000 dilution). Add double carbon dose in 4 splits over 12 hours. Begin 20-30% water exchange with clean replacement water if available (Lin & Chen, 2001; Boyd & Tucker, 2014)
NH₃ 0.05-0.15 mg/L (Stressful): Reduce feed by 30%. Add carbon dose immediately. Monitor pH every 2 hours — small pH rises multiply toxicity exponentially. Consider adding Yucca schidigera extract (1 g/m³) to temporarily bind ammonia (Emerenciano et al., 2017)
NH₃ <0.05 mg/L but TAN rising: Proactive carbon dosing before pH spike. Add NaHCO₃ to stabilize pH at 7.8-8.0. Ensure adequate alkalinity (>120 mg/L) to buffer against pH swings (Boyd & Tucker, 2014)
pH management: Maintain pH 7.5-8.3. Above pH 8.5, NH₃ toxicity increases 3-4×. Below pH 7.0, nitrification slows and heterotrophic efficiency drops. Use NaHCO₃ (not CaCO₃) for rapid pH buffering (Martins et al., 2010)

References: Emerson et al. (1975); Lin & Chen (2001, 2003); Boyd & Tucker (2014); Emerenciano et al. (2017)

⚗️Alkalinity Management

Current alkalinity 0 mg/L

Deficit vs target 0 mg/L

Liming agent dose (correction) 0 kg

Daily maintenance (heterotroph) 0 kg/day

Alkalinity loss this dose 0 mg/L

⚗️ Understanding Alkalinity Dynamics

Alkalinity is the water's buffering capacity against pH changes. In biofloc systems, both heterotrophic bacteria (consuming 3.57 g CaCO₃ per g N assimilated) and nitrifying bacteria (consuming 7.05 g CaCO₃ per g N oxidized) deplete alkalinity continuously. Without replenishment, pH crashes below 7.0, stopping bacterial activity and causing ammonia spikes. Sodium bicarbonate (NaHCO₃) is preferred over calcium carbonate for rapid correction because it dissolves instantly and provides immediate HCO₃⁻ ions.

⚗️ How to Manage Alkalinity

Alkalinity <80 mg/L (CRITICAL): pH crash risk imminent. Add NaHCO₃ in 2-3 splits over 6 hours (never all at once). Recheck pH and alkalinity in 4 hours. Target 140-160 mg/L for startup, 120-150 mg/L for mature systems (Boyd & Hargreaves, 2001; Hargreaves, 2013)
Alkalinity 80-120 mg/L (Low): Add correction dose in 2 splits today. Begin daily maintenance at 0.22 kg NaHCO₃ per kg feed. Monitor weekly — biofloc systems typically lose 20-40 mg/L alkalinity per week (Ebeling et al., 2006)
Alkalinity >150 mg/L (High): Safe but monitor for excessive hardness if using CaCO₃. In marine systems, maintain alkalinity 120-150 mg/L to balance with natural seawater buffering (Boyd & Tucker, 2014)
Daily maintenance: Apply 0.2-0.25 kg NaHCO₃ per kg feed daily, split between morning and evening doses. This replaces heterotrophic alkalinity consumption and stabilizes pH (Hargreaves, 2013; SRAC 4503)
Compound selection: NaHCO₃ (baking soda) dissolves instantly — ideal for corrections. CaCO₃ (agricultural lime) dissolves slowly — better for long-term maintenance. Avoid quicklime (CaO) which causes pH spikes >9.0 (Martins et al., 2010)

References: Ebeling et al. (2006); Boyd & Hargreaves (2001); Hargreaves (2013); Martins et al. (2010); SRAC 4503

💨Oxygen & Aeration

O₂ demand from carbon dose 0 kg

DO drop during peak respiration 0 mg/L

Minimum aerator-hours needed 0 h

CO₂ produced 0 kg/day

💨 Understanding Oxygen Dynamics

Biofloc systems have elevated respiration rates (2-6 mg O₂/L/hour) due to high bacterial biomass. Carbon dosing triggers a bacterial respiration surge that peaks 2-4 hours post-application, consuming 50% of added carbon as CO₂. Dissolved oxygen must stay above 4 mg/L at all times — below 3 mg/L, shrimp become stressed and bacterial nitrification stops. The system cannot survive power outages exceeding 30-60 minutes (Hargreaves, 2013; SRAC 4503).

💨 How to Manage Oxygen Demand

DO <3 mg/L (CRITICAL): Do NOT dose carbon. Maximise all aerators immediately. Add emergency aeration (backup blowers, paddlewheels at 100%). If mortality begins, prepare partial harvest. Never add carbon when DO is below 4 mg/L (SRAC 4503; Hargreaves, 2013)
DO 3-5 mg/L (Low): Hold carbon dosing until DO recovers above 5 mg/L. Increase aeration 30 min before planned dose. Run aerators at 100% for 4 hours post-dose. Consider reducing carbon split sizes and increasing frequency (6 splits instead of 3) (Emerenciano et al., 2017)
Peak respiration management: Start aerators 30 min BEFORE carbon application. Peak O₂ demand occurs 2-4 hours post-dose. For large doses (>5 kg), extend high aeration to 6-8 hours. Monitor DO hourly during peak period (Hargreaves, 2013)
Aerator sizing: Standard requirement: 1-5% water volume per minute airflow. For 1000 m³ pond, use 10-50 m³/min blower capacity. Paddlewheel aerators: 1.5-2.0 kg O₂/kWh efficiency. Calculate total system O₂ demand (shrimp + bacteria + carbon) and size aeration at 150% of peak demand (SRAC 4503)
Emergency preparedness: Install DO alarms with automatic backup power. Biofloc systems fail within 30-60 minutes of power loss. Keep backup generators or battery-powered aerators ready. Response time is much shorter than conventional ponds (Hargreaves, 2013)

References: Hargreaves (2013); SRAC 4503; Emerenciano et al. (2017); Ebeling et al. (2006)

🦠Biofloc Production

Bacterial biomass produced 0 g (today)

TSS contribution per day 0 mg/L

Crude protein in floc 0 g/day

No reading
Enter Imhoff reading in Inputs tab to see biofloc volume status.

Enter Imhoff reading above

🦠 Understanding Biofloc Production

Biofloc is the microbial biomass produced when heterotrophic bacteria assimilate ammonia using supplemental carbon. This biomass contains 30-40% crude protein and serves as a natural food source for shrimp, reducing feed costs by 15-30%. However, excessive biofloc (>500 mg/L TSS) increases oxygen demand, clogs shrimp gills, and creates anaerobic zones. The optimal settleable solids range is 10-15 mL/L for shrimp (measured by Imhoff cone after 15 minutes settling).

🦠 How to Manage Biofloc

TSS >500 mg/L (High): Reduce carbon dosing by 25%. Increase solids removal via settling chambers or foam fractionators. Check Imhoff cone readings daily — target 10-15 mL/L for shrimp. Excessive solids cause gill clogging and oxygen depletion (Hargreaves, 2013; SRAC 4503)
TSS <100 mg/L (Low): Increase C:N ratio to 15-20:1 to stimulate bacterial growth. Verify aeration is adequate to keep solids suspended. Low floc = poor ammonia control. Add probiotic inoculum if starting new system (Avnimelech, 2009)
Imhoff cone monitoring: Measure settleable solids daily at 10:00 AM. 10-15 mL/L = optimal for shrimp. >25 mL/L = remove excess. <5 mL/L = increase carbon. Use 1L cone, 15-minute settling time (SRAC 4503; Hargreaves, 2013)
Floc as feed: Biofloc contains 30-40% protein and can replace 15-30% of commercial feed. Shrimp >5g consume floc effectively. Monitor feed trays — if floc is abundant, reduce pellet feed by 10-15% (Crab et al., 2012; Emerenciano et al., 2017)
Solids removal methods: (1) Settling chambers with 2-4 hour retention, (2) Foam fractionators for fine solids, (3) Periodic draining of central sludge, (4) Resuspend settled solids with paddlewheel repositioning. Never let solids accumulate on bottom — anaerobic zones produce H₂S (SRAC 4503)

References: Avnimelech (2009); Hargreaves (2013); Crab et al. (2012); Emerenciano et al. (2017); SRAC 4503

💰Cost Summary

Carbon source today 0.00

Liming agent (correction + maintenance) 0.00

Total carbon + alkalinity 0.00

Cost per kg shrimp biomass 0.00

💰 Understanding Your Costs

Carbon and alkalinity costs typically represent 8-15% of total production costs in biofloc systems. While higher than conventional ponds, this is offset by zero water exchange costs, improved FCR (1.0-1.2 vs 1.4-1.6), and higher survival rates (80-90% vs 60-70%). The cost per kg shrimp should ideally stay below $0.30-0.50 for carbon + alkalinity combined.

💰 How to Optimize Costs

High carbon costs: Switch to lower-cost sources: molasses ($0.20-0.40/kg) vs sugar ($0.50-0.80/kg). Consider local agricultural byproducts: rice bran, wheat flour, or cassava starch. Verify carbon content with lab test — actual %C varies by source (Avnimelech, 2009; Hargreaves, 2013)
Reduce alkalinity costs: Use agricultural lime (CaCO₃) for maintenance at $0.10-0.20/kg, reserve NaHCO₃ ($0.30-0.50/kg) for emergency corrections. Apply CaCO₃ in slurry form for faster dissolution. Monitor to avoid over-dosing (Martins et al., 2010)
Feed optimization: Lower protein feed (30-32%) reduces carbon requirement by 20-30%. Every 1% protein reduction saves ~0.1 kg carbon per kg feed. Balance with growth performance — test on small scale first (Emerenciano et al., 2017)
Economies of scale: Buy carbon sources in bulk (tonne lots). Negotiate with local sugar mills for molasses. Store in dry, ventilated area — molasses ferments if wet. Shelf life: sugar indefinite, molasses 3-6 months (Hargreaves, 2013)

References: Avnimelech (2009); Hargreaves (2013); Martins et al. (2010); Emerenciano et al. (2017)

📈Trend — Last 14 days

● TAN (mg/L) ● NO₂ (mg/L) ● Dose (kg)

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📐Verified Formulas

1. Nitrogen load from feed

N_feed (g/day) = Feed_kg × 1000 × (Protein% / 100) × 0.16

TAN_excreted = N_feed × Excretion_fraction

0.16 = 1/6.25, N content of protein. Excretion 40-75% (default 50%, Avnimelech 1999).

2. Carbon required (Avnimelech method)

C_needed = TAN_excreted × C:N_target

Mass_source = C_needed / C_fraction

Avnimelech (1999, 2009) — C:N targets 10-20 for biofloc heterotrophic dominance.

3. Un-ionised ammonia (NH₃)

pKa = 0.09018 + 2729.92 / (T + 273.15)

f(NH₃) = 1 / (1 + 10^(pKa − pH))

NH₃-N (mg/L) = TAN × f(NH₃)

Emerson et al. (1975). Salinity correction applied per Bower & Bidwell (1978).

4. Alkalinity correction

NaHCO₃ (kg) = Deficit_mg/L × Vol_m³ × 1.68 / 1000

1.68 = MW(NaHCO₃)/eq.wt.(CaCO₃) = 84/50. Standard stoichiometry.

Heterotrophic alkalinity loss = 3.57 g CaCO₃ / g N consumed

Nitrification alkalinity loss = 7.05 g CaCO₃ / g N oxidised

Ebeling et al. (2006).

5. Oxygen demand

COD_source ≈ 1.07 g O₂/g (sugars), 1.18 (starch), 0.95 (molasses)

O₂_demand = Mass_source × COD × Respiration_fraction

~50% of C respired, ~50% to biomass (Ebeling 2006). Distributed over 8-12 h.

6. Biofloc biomass

Biomass_VSS = N_assimilated × 8.07 g VSS/g N

Crude protein ≈ Biomass × 0.30-0.40

Stoichiometric balance per Ebeling et al. (2006).

🦐Shrimp Tolerance Thresholds

Parameter	Safe	Stressful	Critical
TAN (mg/L)	<1.0	1.0-3.0	>3.0
NH₃-N (mg/L)	<0.05	0.05-0.15	>0.15
NO₂⁻-N (mg/L)	<1.0	1.0-3.0	>5.0
DO (mg/L)	>5.0	3.5-5.0	<3.0
pH	7.5-8.3	<7.0 or >8.7	<6.5 or >9.0
Alkalinity (mg/L)	120-200	80-120	<80
Temperature (°C)	27-31	23-27 / 31-33	<22 or >34

Values for Litopenaeus vannamei. Lin & Chen (2001, 2003); Boyd & Tucker (2014).

🍬Carbon Source Properties

Source	%C	COD/g	Speed
Sucrose (sugar)	42%	1.07	Fast
Molasses	30%	0.95	Fast
Jaggery	40%	1.00	Fast
Tapioca starch	44%	1.18	Moderate
Corn starch	44%	1.18	Moderate
Wheat flour	40%	1.15	Moderate
Rice bran	38%	1.30	Slow
Glycerol	39%	1.22	Fast
Sodium acetate	29%	0.78	Very fast

📚Primary References

Avnimelech, Y. (1999). Carbon/nitrogen ratio as a control element in aquaculture systems. Aquaculture, 176, 227-235.
Avnimelech, Y. (2009). Biofloc Technology — A Practical Guide Book. World Aquaculture Society.
Ebeling, J.M., Timmons, M.B., Bisogni, J.J. (2006). Engineering analysis of the stoichiometry of photoautotrophic, autotrophic, and heterotrophic removal of ammonia-nitrogen. Aquaculture, 257, 346-358.
De Schryver, P., Crab, R., Defoirdt, T., Boon, N., Verstraete, W. (2008). The basics of bio-flocs technology. Aquaculture, 277, 125-137.
Crab, R., Defoirdt, T., Bossier, P., Verstraete, W. (2012). Biofloc technology in aquaculture. Aquaculture, 356-357, 351-356.
Emerson, K., Russo, R.C., Lund, R.E., Thurston, R.V. (1975). Aqueous ammonia equilibrium calculations. J. Fish. Res. Board Can., 32, 2379-2383.
Lin, Y.-C., Chen, J.-C. (2001, 2003). Acute toxicity of ammonia/nitrite on Litopenaeus vannamei. Aquaculture, 224, 193-201.
Boyd, C.E., Hargreaves, J.A. (2001). SRAC Publication 4503: Alkalinity in fish ponds.
Hargreaves, J.A. (2013). Biofloc production systems for aquaculture. SRAC Publication 4503.