What is the best solution to clean white grout between floor tiles?

I used a bleach pen and magic eraser.

Once you get it cleaned up, seal it https://www.todayshomeowner.com/video/sealing-grout-in-tile-floors/

The grout is getting brown because dirt gets ground in. If the grout is silicone, it retains some of its flexibility and dirt is easily ground in. If the grout is cement-based, some of the brown material in it eventually comes to the top, plus the dirt on the floor get the grout the same color as the grout. You can try hydrogen peroxide and baking soda, with your mop water. Neither will hurt your groundwater. Best wishes. ☺️

There is a product called Grout Refresh, that is essentially like repainting the grout lines.

https://www.amazon.com/Grout-Refresh-8oz-Bottle-white/dp/B006IS9B2G

https://www.hometalk.com/categories/clean/bathroom/grout

I find that Mr Clean Magic Eraser works well.

Try a product called Sugar Soap the liquid is best and easier on your hands.

you may have to get a (cheap) grout scraper at your hardware store... then re-grout and SEAL!

Hi there, You can make a thin paste of hydrogen peroxide and baking soda. Apply it to the grout and let it sit for about 10-15 minutes. Scrub with an old toothbrush and rinse clean. If the grout between the tiles has worn down too far, it may be a better idea to first re-grout and then seal. You can also buy grout pens to quickly “recolor” your grout and make them look new again.

Mix a half cup of baking soda with a half cup of hydrogen peroxide. Add a tsp of dish soap.