I have a brand new white tile bathroom shower.  The white grout is staing a gray color.  Some of the grout is cracking but I don’t have any structural cracks. MY tile guy says the water form my shower is staining the grout and if he changes the grout  the stain will just come back. I don’t know if the wall was sealed.  Will sealing keep white grout white or do I have a fundamental water sepage problem causing my grout to discolor?  My new white bathroom looks dingy and it’s brand new.  I would appreciate some advice.