Dr. Tim's First Defense (Saltwater)Chelating agent to detoxify heavy metals Vitamins to fight lateral line erosion Great additive to freshwater dips of marine fish First Defense was developed to help fish adapt to new environments by assisting the fishes' natural immune system. Changing the environment of a fish causes stress that robs fish of essential nutrients and can weaken their immune system. First Defense is scientifically designed to provide stress relief and support the immune