Why are there rust specs in the bottom of my tub?

Enameled porcelain tubs are made from steel that is formed and porcelain coated. The metal structure has a 100% ground coat porcelain enamel coating to prevent rust. Rust spots found are caused by small metal particles that have become lodged in the slip resistant surface. Proper cleaning with a commercial cleaner such as Zudd or Barkeepers Friend can eliminate these spots. It may require repeated cleanings to dislodge these particles.