a lot of water districts have high nitrate levels due to aggi runoff and perculation. usually if that is the case there should have been a letter warning pregnant and nursing mothers to not drink the water. are you on a well or municipal?

if the bond is broken between the chlorine and the ammonia in chlorimines the ammonia will be released. this can happen if a
GAC filter's carbon is to weak to attract the chlorimines as a unit or a chlorine neutralizer is used that is not capable of neutralizing the ammonia. an API test kit can handle it. i'm not sure about some of the others giving false readings. the bottle of neutralizer should tell you.