Am putting our PPR on the rental market and have realised that no matter how hard/often I clean the main shower it has grey steaks (like water runs) down it I cant get off. I have heard this could be a type of glass cancer, the townhouse is only 6yo and we have had it for 1yr. Anyone any ideas how I can clean it further. Have tried Easy Off Bam and Ajax creme cleanser. Any help appreciated.