The Rally label lists three active ingredients that have been proven effective in parasite control in aquaculture operations and tropical fish farms: acriflavine, aminoacridine and formalin. Virtually all hobby aficionados are familiar with formalin, most are probably at least aware of acriflavine, and the pharmaceutically well informed probably know about aminoacridine.
The end result is that Rally is an extremely effective water treatment for the control of many external parasites including dinoflagellates (e.g., marine velvet, clownfish disease), flukes and gram-negative bacteria (e.g., bacterial fin/tail rot, superficial sepsis, etc). Rally is, at best, marginally effective against I. multifiliis and C. irritans, but extremely useful in preventing the secondary bacterial infections that often accompany severe ich infestations. Rally is not harmful to fish, invertebrates, corals, etc., nor does it affect the symbiotic algae vital to corals or other beneficial bacteria. Beta site tests in shops around the United States have shown the combined use of Rally with Kick-Ich or a variety of common antibiotics is not harmful to fish, invertebrates, corals or biological filtration.