Sterazin is used or the control of gill & body parasites which cause fish to flick when no symptoms are visible to the unaided eye. Sterazin will also aid the control of internal parasites such as Round Worm Thread Worm & Intestinal Worm. In order to destroy the parasites in all stages of their life cycle you will need to use the product on days 1 3 6 8 & 10. STERAZIN may also be used to aid the sterilisation of aquatic plants & is highly biodegradable. Do not use when crustaceans echinoderms rays seawater sharks pirahna sturgeon or sterlets & related species are present. In these instances use Waterlife Paragon. a 60ml bottle is sufficient for a 5 day coarse for 180 Litres.