I like the comparison of grout cleaners in this video. When it comes down to grout cleaning getting a tough cleaner that has a higher pH is going to do a good job getting the soil out of your grout. The key is scrubbing the grout with an abrasive brush. You can even use water and dish soap as a grout cleaner if your alright with getting on your hands and knees and scrubbing the grout line like they do in the video. It's a lot of labor but very effective.
If you want clean grout lines but don't want to have soar knees I recommend giving Chem-Dry of Tampa FL a call we professionally clean grout and tile. ?using a proprietary cleaning solution and high pressure extraction we remove the soil embedded in your grout.