A study was performed at the North Carolina State University, College of Veterinary Medicine, to assess the safety and efficacy of Melafix, an aquarium product produced by Mars Fishcare Incorporated. Studies were carried out on the goldfish (Carassius auratus), a freshwater species, and the false percula clownfish (Amphiprion ocellaris), a marine fish. Animals were monitored closely and evaluated microscopically after exposure to Melafix according to the label directions for a period of 28 days. Water-quality parameters were monitored on a daily basis. The use of Melafix on goldfish and clownfish appears to be safe as no adverse effects were noted during the experimental period. The results also showed that Melafix has no effect on the water-quality parameters tested. In vitro efficacy studies were conducted by determining the minimum inhibitory concentration and minimum bactericidal concentration of Melafix on various pathogens. The study revealed that Melafix had no significant bactericidal or inhibitory effect on any of the pathogens tested. This observation suggests that anecdotal benefits of Melafix are not owing to antibacterial activity. This topic requires further research and possibly an in vivo study.