Nutrafin Cycle Biological Aquarium Supplement. Nutrafin Cycle - Biological Aquarium Supplement features a high-concentration formula that immediately establishes a safe biological aquarium environment. Cycle goes to work fast, releasing massive amounts of beneficial bacteria that eliminate toxic ammonia and nitrites and creating a biologically well-balanced aquarium for healthy fish to thrive. It is also ideal for quickly establishing safe and essential conditions in new aquarium setups, so that you can introduce fish to new aquariums immediately. Regular application helps to competitively exclude the establishment of undesirable bacteria in aquariums. Cycle provides consistent results thanks to our unique and proprietary bio-floc technology that preserves product stability, efficacy and shelf life. High-quality production processes ensure that every container of Cycle contains pure, safe bacterial colonies free of undesirable contaminants. Cycle is an all-natural product that will not harm plants, animals or humans. It does not require refrigeration. For fresh and saltwater use. Immediately establishes safe biological aquarium environment Powerful responsive ammonia and nitrite elimination For fresh and saltwater use Available Sizes: 120 mL (4 fl oz) / 250 mL (8.4 fl oz) / 500 mL (16.9 fl oz) / 2 L (2.1 qt).