How can I refresh grout lines on a marble floor?

Here are 10 cleaners that you make using everyday products, and they’re non-toxic.

https://brendid.com/ultimate-guide-to-cleaning-grout-and-tile/

Did you try bleach? When all else fails just paint the grout. I used white oil based 8 years ago, still looks great.

Clean well then paint with exterior paint and seal once dry.

Hello. Heres some other recommended cleaners

The Best Way to Clean Grout-EVER!!! | Hometalk

https://www.hometalk.com/diy/clean/bathroom/the-best-way-to-clean-grout-ever-2295735?expand_all_questions=1

https://www.hometalk.com/diy/clean/floors/homemade-grout-cleaner-recipe-41693881?expand_all_questions=1

https://www.bobvila.com/articles/cleaning-grout/#.Wi6YzKZOmf0

https://www.hometalk.com/search/posts?filter=clean%20grout

Additionally

Painted Tile Grout Refresh with grout pen

https://www.blesserhouse.com/painted-tile-grout-refresh/

Grout cleaning and grout removal and replace it

Here’s a Hometalk link for you to consider. Hope this helps

https://www.hometalk.com/diy/clean/bathroom/how-to-clean-grout-and-install-new-grout-that-won-t-stain-23803774

This works well for grout lines: https://amzn.to/34yOt0E

Hope this Helps! Jeremy - https://do-daddy.com

This product works well for both tile and grout: https://amzn.to/34yOt0E

Hope this Helps! Jeremy - https://do-daddy.com