Waterlife sterazin stops fish flicking and rubbing. Treats gill and body parasites along with internal worms in most tropical and cold water fish.. Sterazin should not be used with crustaceans, echinoderms, rays, seawater sharks, piranha, sturgeon or sterlets and other related species use waterlife paragon . It is also harmless to plants, and filtration bacteria.. 100Ml treats up to 200 litres over a 5-day course.. 250Ml treats up to 500 litres over a 5-day course.