Sea-Klear Natural Clarifier works brilliantly, completely preventing scum formations and removing heavy metals such as copper, iron and maganese. Sea-Klear greatly improves filter efficiency too. Made from crab shells, not oil wells, one gallon will remove one part per million of metal in a 20,000 gallon pool. Just distribute Sea-Klear over the surface of the pool. It is so safe that it can be used while swimmers are in the water. Retest for metals after one filter cycle. Compatible with all sanitizers including Baquacil® and SoftSwim™. Available in blue or green.