CAL BLOCKIs a safe, non toxic, invisible, multi surface protectant that is specifically formulated to "Block" calcium and hard scale from building up and damaging your pool tiles and water features, allowing future calcium to be easily removed off any treated surface. Easily applied to glass, porcelain and ceramic pool tile, concrete, rock features, travertine and concrete pavers, metal and more. Apply every 3 6 months to greatly reduce calcium, scale,