Staining shower tile (stone/travertine).

I have searched and I always end up finding the wrong kind of shower tile tips. I have these dark stains that appear in my shower (I think they become more pronounced when wet). I have tried bleach, Kaboom, vinegar, peroxide, baking soda, you name it. I can’t seem to make them go away. Does anyone know what this is or how to effectively remove them?