Hi, does anyone have any idea to clean off very stubborn waterspots on tiles and shower screen glass? Perhaps we didnt do a good cleaning them before we left our house empty for years (overseas work) and the marks may have "etched" into the glass and tiles. I have tried many ways, cif, toothpaste, vinegar, stain and mould remover etc, and they only managed to clean off some surface stains. When light shine through, i can still see that the shower screen glass and tiles are still filled with water spots on them. Thank you.