Can you share advice on how to handle the restoration of a honed travertine tile shower? The shower was built in 2002 and purchased by the existing owner in 2003. It has three walls with a total width of 12 feet and the tiles extend up 9 feet high. Nothing has ever been done to the shower by the previous or current owner other than wiping down the walls with over the counter cleaners. Each wall has what looks like mildew staining in the first tiles from the floor. I came up empty when scraping the walls wtih a single edge razor blade. Nothing came off of the tiles. The mildew looking staining seems to be embedded in the stone, and there are also mineral staining on the tiles from the shower head down. I've enclosed photos of the "mildew" staining. Any advice would be appreciated. This would be my first travertines wall restoration and would appreciate guidance in the proper way to approach. Thank you all in advance.