Ammonia and Ammonium and their relationship

ammonium is also less toxic than ammonia; this is why you should not put an air stone into a fish's shipping bag if you ever get fish shipped to you. an air stone will cause CO2 to be driven out from the water, and cause the pH to rise quickly. this, in turn, causes the ammonia level to skyrocket which can be fatal for your fish.

And is the danger of drip acclimation after a long shipping.