Maintain healthy levels of copper in your fresh or saltwater aquarium with API Copper Cu+ Fresh & Salt Water Aquarium Test Kit. Copper in small amounts is an essential mineral for aquatic plants and fish. It helps to promote photosynthesis in plants and prevent anemia in fish. Copper is also a common treatment for many parasitic infections. Plants and fish extract copper from aquarium water, so it's important to test levels often to ensure levels are healthy, especially when medicating. This test kit measures 0 to 4 mb/L or ppm of copper. Just fill the test tube and add a few drops of the test solution. Then compare results with the included color chart and follow the recommendations if action is needed.