Total Ammonia vs. Toxic Ammonia
By Christopher Burns
Many ammonia test kits on the market test for total ammonia, which is the combination of highly toxic ammonia molecules (NH3) and relatively harmless ammonium molecules (NH4+). Toxic ammonia is a percentage of the total ammonia measured, and the percentage is based on the pH and the temperature of the water. Table 1, below, gives the multiplier for a wide array of pH and temperature values.

To use the table, first determine if your test kit tests for toxic or total ammonia. If it tests for total ammonia, then take the measured amount and multiply that by the value found in the table for your tank's pH and temperature. The result is the amount of toxic ammonia in the water.

For example, let's take a tank with the following measurements:

Total ammonia = 1.25ppm
pH = 8.2
Temperature = 80°F

The corresponding conversion factor for the given pH and temperature by the table below is approximately .0940
Then we multiply: 1.25ppm total ammonia × .0940 = .118ppm of toxic ammonia.

To determine if your test kit tests for toxic or total ammonia, you can either check the instructions carefully, or test water that you know contains 0ppm of toxic ammonia and see what your kit registers. If it shows ammonia, then you are probably measuring total ammonia.

Table 1
pH Temperature
20C/68.0F 21C/69.8F 22C/71.6F 23C/73.4F 24C/75.2F 25C/77.0F 26C/78.8F 27C/80.6F 28C/82.4F 29C/84.2F
7.6 .0157 .0169 .0181 .0194 .0207 .0222 .0238 .0254 .0272 .0290
7.8 .0247 .0265 .0284 .0304 .0325 .0347 .0371 .0397 .0425 .0452
8.0 .0386 .0413 .0442 .0473 .0505 .0539 .0576 .0614 .0657 .0697
8.2 .0599 .0639 .0683 .0730 .0778 .0829 .0883 .0940 .1002 .1062
8.4 .0917 .0977 .1041 .1109 .1179 .1253 .1331 .1412 .1500 .1585
8.6 .1379 .1465 .1555 .1651 .1748 .1850 .1958 .2067 .2186 .2298

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