Aquarium Systems SeaTest NH4 Ammonia (40 Tests) test for ammonium (NH4), a chemical compound which is normally converted into nitrites and then into nitrates in the nitrogen cycle. For freshwater and seawater. Maximum value recommended: 0.25mg/l (this value is already deemed hazardous in seawater). For approximately 40 tests. Graduated 7-colour colour scale (0; 0.2; 0.5; 1; 2; 3; 5mg/l). For a result accurate down to 0.01 mgl, use the Aquarium Systems NH4 test in combination with SeaTestControl. This device is especially and uniquely calibrated for Aquarium Systems tests. Caution, observe the precautions for use.