Sea-Klear 4-in-1 Clarifying Water Treatment for Spas clarifies brilliantly, completely preventing scum formations while removing heavy metals such as copper, iron and maganese. Made from crab shells, not oil wells, Sea-Klear greatly improves filter efficiency too. Just distribute Sea-Klear over the surface of the spa. It is so safe that it can be used while people are in the water. Retest for metals after one filter cycle.