What really works?
Start with vinegar and a scrub brush. Here's a link with more ideas:
I use Clorox Toilet Bowl Cleaner for grout lines and it works great for me since I use it on my floor tiles. I have tried many other recommended methods and none worked as well as this.
Toilet bowl cleaner removes some of the surface grout.
Hi, you have a common cleaning problem with so many kitchen and bathroom tiles used in homes now. I have chosen one for you, but there are many if you click on "explore projects" then "clean" then "bathrooms" then "grout." Hope this helps: https://www.hometalk.com/2295735/the-best-way-to-clean-grout-ever
I use a soap scum remover such as scrubbing bubbles or lysol power bath. This breaks down the soap/mineral bond that is trapping the discoloration. Then you can bleach it. Or alternatively, you can use a grout pen to stain it a different color.
The REAL SOLUTION, however, is to seal the grout prior allowing any build up. Once you clean your grout adequately, seal it.