This summarizes the facts concerning nitrifying bacteria. References follow if anyone wants to read the scientific studies.
Nitrifying Bacteria
Nitrification is the oxidation of ammonia/ammonium to nitrite and then the subsequent oxidation of nitrite to nitrate; this is performed by two groups of bacteria known collectively as nitrifying bacteria or nitrifiers. True nitrifying bacteria are autotrophs; they use chemosynthesis to manufacture their energy by using oxygen plus nitrogenous waste (ammonia or nitrite) and carbon (from CO2). There are several different bacterium species involved, all in the family Nitrobacteraceae, that carry out this function in soil, and it used to be thought that these, particularly Nitrosomonas europa and Nitrobacter, were the nitrification bacteria in freshwater. But Dr. Timothy Hovanec led the team of scientists that proved this to be a mistaken assumption. Ammonia is converted to nitrite by bacteria of the Nitrosonomas marina-like strain [2] and nitrite is converted to nitrate by bacteria closely related to Nitrospira moscoviensis and Nitrospira marina. [3] Subsequent scientific studies by other scientists on wastewater nitrifying bacteria confirm this data.
[2] Paul C. Burrell, Carol M. Phalen, and Timothy A. Hovanec, “Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, December 2001, pp. 5791-5800.
[3] Hovanec, T. A., L. T. Taylor, A. Blakis and E. F. DeLong (1998), “Nitrospira- Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, Vol. 64, No. 1, pp. 258-264.
There are no so-called bacterial supplements that work in one day, with the exception of the two which hold patents. Dr. Tim's One and Only, and Tetra's Safe Start; these were developed by Dr. Hovanec. As for API's Quick Start, it does not contain the second stage nitrite-oxidizing bacteria so it will not "cycle" an aquarium. Dr. Hovanec tested several of these so-called cycling products and found that at best one or two quickened the cycling by one or two days (out of 4-8 weeks), but most did absolutely nothing.