LaMotte Fresh Water Aquaculture User Manual
Page 13
13
Ammonia in water occurs in two forms: toxic unionized ammonia (NH
3
) and the
relatively non-toxic form, ammonium ion (NH
4
+
). This test method measures both
forms as ammonia-nitrogen (NH
3
-N) to give the total ammonia-nitrogen concentration
in water. The actual proportion of each compound depends on temperature, alkalinity,
and pH. A greater concentration of unionized ammonia is present when the pH value
and salinity increase.
1. Consult the table below to fi nd the percentage that corresponds to the temperature,
pH and salinity of the sample.
2. To express the test result as ppm Unionized Ammonia Nitrogen (NH
3
-N), multiply the
total ammonia-nitrogen test result by the percentage from the table.
3. To express the test result as ppm Ionized Ammonia Nitrogen (NH
4
-N), subtract the
unionized ammonia nitrogen, determined in Step 2, from the total ammonia-nitrogen.
Percentage of Free Ammonia as (NH
3
) in Freshwater
1
(FW)
and Seawater
2
(SW) at varying pH and temperature.
10°C
15°C
20°C
25°C
pH
FW1
SW2
FW
SW
FW
SW
FW
SW
7.0
0.19
0.27
0.40
0.55
7.1
0.23
0.34
0.50
0.70
7.2
0.29
0.43
0.63
0.88
7.3
0.37
0.54
0.79
1.10
7.4
0.47
0.68
0.99
1.38
7.5
0.59
0.459
0.85
0.665
1.24
0.963
1.73
1.39
7.6
0.74
0.577
1.07
0.836
1.56
1.21
2.17
1.75
7.7
0.92
0.726
1.35
1.05
1.96
1.52
2.72
2.19
7.8
1.16
0.912
1.69
1.32
2.45
1.90
3.39
2.74
7.9
1.46
1.15
2.12
1.66
3.06
2.39
4.24
3.43
8.0
1.83
1.44
2.65
2.07
3.83
2.98
5.28
4.28
8.1
2.29
1.80
3.32
2.60
4.77
3.73
6.55
5.32
8.2
2.86
2.26
4.14
3.25
5.94
4.65
8.11
6.61
8.3
3.58
2.83
5.16
4.06
7.36
5.78
10.00
8.18
8.4
4.46
3.54
6.41
5.05
9.09
7.17
12.27
10.10
8.5
5.55
4.41
7.98
6.28
11.18
8.87
14.97
12.40
1
Freshwater data from Trussel (1972).
2
Seawater values from Bower and Bidwell (1978). Salinity for Seawater values = 34 ppt at an
ionic strength of 0.701 m.
FOR EXAMPLE:
A fresh water sample at 20°C has a pH of 8.5 and the test result is 1.0 ppm as total
Ammonia-Nitrogen.
1. The percentage from the table is 11.18% (or 0.1118).
2. 1 ppm total Ammonia-Nitrogen x 0.1118 = 0.1118 ppm Unionized Ammonia-
Nitrogen
3. Total Ammonia-Nitrogen
1.0000 ppm
Unionized
Ammonia-Nitrogen -
0.1118
ppm
Ionized
Ammonia-Nitrogen
=
0.8882
ppm
AMMONIA IN AQUARIUMS