Saturationa; > 5 mg/L
Saturation; > 5 mg/L
< 12 mg/L
< 12 mg/L
TAN (total ammonia nitrogen)b
Toxic un-ionized ammonia (NH3)b
< 20 mg/L
< 70 mg/L
Total alkalinity (carbonate fraction)
> 100 mg/L CaCO3
> 250 mg/L CaCO3
Total hardness (Ca and Mg primarily)
> 20 mg/L CaCO3
> 250 mg/L CaCO3c
If source water is from municipal water supply:
Total chlorine (free chlorine + chloramines)
aDissolved oxygen in ponds will fluctuate on a diurnal basis. Concentrations < 5 mg/L are dangerous. Mortality will be species-specific and related to time of exposure but may be observed at ≤ 4 mg/L. Oxygen saturation at room temperature (25°C [77°F]) and sea level will be 8.27 mg/L in freshwater and 6.75 mg/L in seawater (35 ppt or chlorinity of 20 ppt).
bUnder most circumstances, freshwater fish can tolerate TAN concentrations < 1 mg/L, whereas saltwater fish will usually tolerate TAN concentrations < 0.5 mg/L. Un-ionized ammonia concentrations < 0.05 mg/L are not considered harmful, with the caveat that there will be species-specific and situation differences in tolerance.
cTest kits may only provide results in Nitrite-Nitrogen. Not generally measured in marine systems.
dTest kits may only provide results in Nitrate-Nitrogen.