Gill Wash contains an antibacterial surface-active agent that helps remove excess mucus from the skin and gills. When fish have been irritated by parasites or bacterial infection they produce mucus as a means of easing the irritation. This can lead to a build up of mucus that interferes with the normal gill and skin function. Bathing in Gill-Wash gently removes the excess mucus to allow the fish to breathe more easily at the same time combating any infection that may be present.