Porous tile and grout surfaces are not maintainable. Emulsified dirt, mold and bacteria become embedded in the porous surface with each nightly mopping. "Cleaning" tile and "cleaning" grout lines by mopping have actually intensified your problem. The main reason for grout to get discolored is dirty mop water over a period of time will turn/stain even the lightest colored grout dark. These stains are very hard to remove as well as being an excellent breeding ground for bacteria, mold & mildew.
Using high pressure and heat can help remove the dirt and bacteria in the porous surface of the tile and grout restoring to its original look as well as disinfect.
Katy Pros is your local source for pre-qualified service providers in Katy Texas.