Keep your aquatic life thriving with Dr. Tim's Aquatics First Defense Freshwater Aquariums Stress Relief & Immune Support. Recommended for use during partial water changes， during disease treatments， or when fish are showing signs of stress， this support is your first line of defense for healthy fish. Containing a mixture of vitamins and immunostimulants， they work together to support the immune system， promote healing， and repair wounds. First Defense also neutralizes chlorine and chloramine， buffers against pH changes， and detoxifies heavy metals—making it an all-around great product for fishkeepers to have on hand.