Merck Manual

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“Normal” Reference Ranges for Routine Water Quality Analysis

“Normal” Reference Ranges for Routine Water Quality Analysis

Parameter

Freshwater

Saltwater

Dissolved oxygen

Saturationa

Saturation

Carbon dioxide

<12 mg/L

<12 mg/L

pH

6.5–9.0

7.8–8.3

TAN (total ammonia nitrogen)b

0 mg/L

0 mg/L

Toxic un-ionized ammonia (NH3)b

0 mg/L

0 mg/L

Nitrite

0 mg/L

0 mg/L

Nitrate

<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 CaCO3

If source water is from municipal water supply:

Total chlorine (free chlorine + chloramines)

0 mg/L

0 mg/L

Free chlorine

0 mg/L

0 mg/L

a Dissolved 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).

b Under most circumstances, freshwater fish can tolerate total ammonia concentrations <1 mg/L, whereas saltwater fish will usually tolerate TAN <0.5 mg/L. Un-ionized ammonia concentrations <0.05 mg/L are not considered harmful.