| 75 TESTS This kit measures total (NH3 and NH4+) and free ammonia (NH3 only) down to 0.05 mg/L and is virtually interference free in marine and fresh water. Free ammonia is the toxic form of ammonia (vs. ionized Ammonia NH4+ which is non-toxic) and thus it is much more important to keep an eye on the level of free ammonia in your system. | 
