I always use a neutral Ph cleaner on Travertine called Kryptonite from Steam Brite. It normally does the trick but got a really high end residential home and they used unusual wide/large grout lines and they are really dirty. It is a polished travertine and grout isn’t sealed (so she says) but it isn’t cleaning up all that well. Tempted to use Grout Master but can’t afford to screw up tile. Did a small test and looks great but not sure about doing whole job. Its over 2500 sq feet. Advice/thoughts???