Do not get the Fritz dry ammonium chloride- it is enough to cycle 100s of tanks. Fritz also makes something called Fritz Aquatics Fishless Fuel. This is similar to Dr. Tim's Ammonium Chloride. Buy either of these online from Amazon.
Before such products were available I used plain old household ammonia with nothing else in it but some surfactants. It worked fine but back then we used a drops/10 gal. dosing method which was not really accurate.
Juts as an FYI i have the Fritz dry stuff because I have to cycle too many tanks or filters fast. But I also have the Dr. Tim's for use on only one or two tanks. When I used the last of my Dr. T's, I used his bottle to make my own solution from ro/di water and the Fritz powder. I got it pretty close to the same concentration as is in the Dr. Tim's.