Travertine Stone

Travertine shower mold – how to get out without damaging the stone?
I have an unfinished travertine shower. In recent years, a section (near shore) is gray – the gray grows gradually. I think the mold got into it. The problem is that all the dead mussels bath products specifically that are not for use on travertine stone and unfinished stone in March. How can I get the stone clean and free of mold without breaking the bank? Ideas? I know there are products for cleaning the stone – but – you have to kill mold?
Try using Vital Oxide his safe on almost any surface.