I can't remember exactly what the title was but something along the lines of 'Aquarium Set Up For Beginners' it was written at least 20 years ago most likely more (I do not have the book-it's in the library and i read it when I am waiting for my brother). The book said it killed both good and bad bacteria. It also said that although it is more popular to add it into marine set ups, adding it to freshwater set ups can be done as well. I wasn't thinking of adding it to my aquaria, I just wanted to know if it still exists since I was reading an older book and anything more about it.
Oh and ad_smith, I believe what is talked about in the link is the same stuff.