"The most difficult part of the fishless cycling procedure, according to many postings on the message boards, involves finding a good source of ammonia. Ammonia used should be free of surfactants, perfumes, and colourants. Unfortunately, not everyone has access to ACS grade ammonium hydroxide. Always read the ingredients on the bottle. The best sources for Pure or Clear Ammonia are discount grocery stores or hardware stores. Often, the no-name brand is the stuff you're looking for. Some other people have reported success with the following brand names of ammonia: Top Crest or Whirl Clear Ammonia. To paraphrase RTR: If it doesn't list the ingredients, or say Clear Ammonia (or Pure Ammonia or 100% Ammonia, or Pure Ammonium Hydroxide), then leave it on the shelf and look elsewhere. Shake the bottle if you're not sure about it... ammonia with surfactants will foam, while good ammonia will not."
http://www.tropicalfishcentre.co.uk/Fishlesscycle.htm