Parazin is a unique and revolutionary parasticide, requiring only one dose per infestation. It treats fish lice, anchor worm, gill maggots and other crustacean predators and parasites. It is not harmful to filtration bacteria, fish or plants. Please read instructions fully before use, switch off UV sterilisers and remove carbon/ammonia removers. For use in tropical freshwater and coldwater aquariua. Please note: not for use with crayfish, crabs, shrimps, lobsters or related species. 20 Tablets - up to 450 litres.