Borgmann Aquaponics Hydroponics
The Decisive Factor: pH Value and Temperature
The toxicity of total ammonium (NH4+ + NH3) depends on the proportion of toxic Ammonia (NH3), which increases with rising pH value and temperature.
Conversion
Total Ammonium as N: NH4-N = NH4+ × 0.776
Ammonia Fraction: % NH3 = f(pH, Temperature, Ionic Strength) → Must be determined using tables or calculation tools.
Practical Guideline Values for Aquaponics
Recommended Chronic Exposure (NH3-N):
- Salmonids (Trout, Salmon): < 0.0125 g/m³ (12.5 µg/L)
- Cyprinids (Carp, Tilapia): < 0.031 g/m³ (31 µg/L)
These values should never be permanently exceeded.
Practice-Oriented Guideline Table
| Parameter & Fish Group | Target Range (Chronic Exposure) | Critical Range (Stress, Growth Impairment) | Acute Lethal Range (LC50-96h) |
|---|---|---|---|
| Ammonia (NH3-N) Salmonids |
< 0.0125 g/m³ | 0.03 – 0.1 g/m³ | > 0.2 g/m³ |
| Ammonia (NH3-N) Cyprinids |
< 0.031 g/m³ | 0.05 – 0.2 g/m³ | > 0.6 g/m³ |
| Total Ammonium (NH4-N) Example at pH 8 & 25°C |
< 0.5 g/m³ (results in ~0.028 g/m³ NH3-N) |
> 1.0 g/m³ (results in ~0.056 g/m³ NH3-N) |
Highly variable |
Practical Recommendation for Your Aquaponics System
- Monitoring: Continuously measure Total Ammonium, pH value, and temperature. Calculate the NH3 concentration from these.
- Upper Limit: Aim for Total Ammonium (NH4-N) values below 1.0 g/m³, ideally < 0.5 g/m³.
- pH Control: A rising pH value (e.g., due to plant activity) can suddenly create toxic conditions at the same ammonium concentration.
- Biofilter: The nitrifying biofilter (NH4+ → NO2- → NO3-) is your most important safety device. Always keep it performing optimally.
Conclusion: The EU water guideline values (e.g., limit value 0.776 g/m³ NH4-N for salmonids) are not directly applicable for aquaponics and are too lenient. Work with the stricter, practice-oriented values from aquaculture.
Note: LC50 values (Lethal Concentration for 50% of animals over 96 hours) are species- and environment-specific. The stated lethal ranges are approximations for robust cultured strains. Sensitive species or juveniles can die at lower values.
The conversion between NH4+, NH4-N and NH3-N is concentration-dependent. For precise calculations, please use specialized aquaculture calculators.
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