Zym Bac - Nitrifying Bacteria 4 oz Establishes biological filtration quickly and helps prevent "New Tank Syndrome" Contains only naturally occurring specially cultured beneficial bacteria. Rapidly seeds biological filters Corrects ammonia/nitrite imbalances Improves aquarium water conditions naturally. Is safe for fish. Extends longevity of aquatic life. Does not affect pH. Zym Bac contains species of bacteria that are beneficial when starting or accelerating the nitrogen cycle of biological filtration, particularly in those aquariums in which the proper bacteria are in short supply or are not naturally present. Zym Bac will greatly bolster the number of naturally occurring nitrifying bacteria present, resulting in shorter cycle times and more efficient biological filtration. Zym Bac will help replace bacteria lost due to medicating, changing filter media, adding new fish, etc. The bacteria provided in Kordon Zym Bac are particularly effective, hardy, and beneficial over the long term in aquarium keeping.