You need Aqua Mix Heavy Duty Tile & Grout Cleaner. Pre Wet the tiles then apply the Aqua Mix HDT&G let it dwell for ten minutes keeping it wet then scrub it with a rotary scrubber and emulsifying pad and vac off. Rinse with warm water and repeat. Then seal the tiles and grout with eiither Aquas Mix Sealers Choice Gold if you want the tiles to look the same or Aqua Mix Enrich N Seal if you want a permanent wet look.
Kev Martin
Tiling Logistics
Marble Life Ltd