Hi last year we moved into a house and hired someone to regrout our shower stall because its an old house and the old grout was all deteriorated and the precious owner ignored the issue for years, which caused the water leaking through the shower to the bedroom. It was a nightmare.
The company used an epoxy grout called Mapei Kerapoxy and resolved the issue.
However, just after 4 months, we can see mold starts forming on the grout. This happens even if we turn on the exhaust fan while bathing. Two issues we are struggling to resolve:
1) Is there any non erosive product that can clean and wont errode / damage our new grout?

2) Also we are considering to install an exhaust fan on the bathroom window. Now our bathroom exhaust fan is connected to the ceiling space, but our roof is metal. Unlike tile roof, the ceiling space under metal roof is quite enclosed without sufficient airflow. It seems extracting moisture to the another enclosed space is not quite a good idea. Any suggestion?
Thanks in advance.