1 to 3 mg/l of ammonia is good for spirulina cultures. If ammonia levels exceed 20mg/l NH4+it can be radical for spirulina.
This test allows you to control the deficiencies and excesses of the most important element for spirulina: nitrogen. It is particularly important in the reasoned culture of spirulina and in cultures based on organic inputs (whose composition in nitrogen brought is not precisely known).
This test is also very important for aquariums to check that there is no more than 3mg/l of NH3 in the water: levels above this are very dangerous for fish.