Borgmann Aquaponics Hydroponics
Dimensioning and balancing fish production & biofiltration
1. Fish Production
2. Biofilter
Filter Parameters (overwritable)
? Growth-, Feed- and Filter-Load Curve
⚠️ Note on simplification
- FCR-based feed quantity: Feed = Weight gain × FCR
- NH₄-N from feed (not from fish weight):
NH₄-N = Feed × Protein% × 0.16 × N excretion%
(0.16 = N content in protein, species-specific excretion 65-75%) - P-Retention:
Bony fish: 30-40% P remains in the fish
Shrimp: only 10-15% P retention - Feed Curve:
Both extremes are displayed (FCR Extensive & Intensive). This allows you to see the comparison to the actual feeding requirements, how far your System is optimized. - More Details about here
Temperature dependence of biofilter performance
We used the following values to calculate the biofilter performance
- < 2°C = deadly for Filter
- < 10°C ~ 30% Performance
- < 15°C ~ 50% Performance (Forelle !)
- < 20°C ~ 75% Performance
- < 25°C ~ 100% Performance
- < 30°C ~ 110% (a bit better)
- > 30°C ~ 90% (to hot !)
- > 40°C = deadly for Filter
Half an hour of contact with the filter medium is considered optimal (~95%).
- > 5 Min ~ 30% efficiency
- > 10 Min ~ 60% efficiency
- > 15 Min ~ 80% efficiency
- > 30 Min ~ 95% efficiency
- Hardly any further increase beyond that
CSB
COD (Chemical Oxygen Demand) measures the total amount of all oxidizable organic and inorganic substances in water through chemical oxidation with dichromate. In aquaponic systems, COD primarily comes from leftover feed, fish waste, and dissolved organic compounds - a high COD value (>50 mg/L) indicates overloading and can lead to oxygen deficiency.
BOD5
BOD5 (Biochemical Oxygen Demand after 5 days) measures only the biodegradable organic substances that microorganisms can break down within 5 days under aerobic conditions - it is therefore an indicator of the actual load on the biofilter. BOD5 is typically 60-70% of the COD value; a BOD5 >30 mg/L in aquaponic systems signals that the biofilter is working hard and may be overloaded.
Rule of thumb for aquaponics:
- COD/BOD5 ratio ~1.4-1.5: The closer to 1.0, the higher the proportion of biodegradable substances
- Biofilter primarily breaks down BOD5, not the entire COD
- Excess COD slowly accumulates in the system → regular partial water changes are important
? Fish Production
? At stocking (cycle start)
? Biofilter Peak Load
A rising pH value (e.g., due to plant activity) can suddenly create toxic conditions at the same ammonium concentration:
Ammonia ⇒ Nitrite ⇒ Nitrate
? At Harvest (cycle end)
? Biofilter-Capacity
⚖️ System Balance
? Summary
Important:
NH₄-N excretion rates are not species-specific constants; they depend heavily on:
Feeding rate & protein content, temperature, body weight, FCR rate, stress / activity / movement, etc.
Stocking Densities
Important legal notes:
As of 26.01.2026, there are no uniform, EU-wide binding stocking density regulations for Aquaponics
regarding the fish species listed here. The regulation is multifaceted and based on several legal areas.
The permissible density results from the interplay of national animal welfare law, fertilizer law, and the practical
limits of your specific aquaponics system design. Consultation with the responsible veterinary and environmental authorities
prior to planning is essential.
For validated information, please schedule a consultation!
All information without guarantee. Use at your own risk. Any liability is excluded.
BiFiFil 0.2.24-en © by Helmer Borgmann 2026
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