It's impossible to buy ammonia around here that doesn't have soap or a sudsing agent added, so be wary!
-Matt
Thus my recommendation for a pure ammonia source... I recommend you use DrTim's Aquatics Ammonium chloride... All of the ammonia I found in grocery, hardware, and other big box stores have other things in it, some times labeled surfactants. Long story they are cleaning compounds, and you do not want them in your tank!