Brush the tile line vigorously in combination with acid. Use a metal brush with a tile cleaner. Then, use a pumas stone or metal brush again. For hardened or thick caking of calcium stains on tile, a “bead blasting” method may be recommended. Sodium bicarbonate or finely ground glass will be aimed at the stains for removal. This process is safe on pool surfaces and tile, and when applied professionally, has minimal clean up.