The posted link to http://www.wisezipper.co/log.php didn't work for me.
I have seen the work of grout sealers before, and they leave streaks on the tiles, and in time require resealing.
Understand the problem: Grout is a cement product, and breathes and soaks. Often the mold and mildew that appears on grout is deeply-embedded, and must be removed from within, yet general purpose cleaners such as chlorine bleach, while effective on surfaces, do not effectively remove the root cause without a strategy.
Soaking helps because it penetrates, but you cannot expect a single wash cycle to do the trick.
I like the youtube spinning brush idea that was posted above [thumbs up!], as it agitates and the vibrations allow the chemical compounds to penetrate deeper and be more effective.
If Scrubbing Bubbles is not easily and affordably accessible then I recommend combining chlorine bleach with a bleach-based cleaning powder such as Ajax or Comet to produce a wet creamy solution, and wiping it on the tiles and grout, then letting it sit for a while. Return with a brush or drill-brush and agitate (careful not to let it spray all over you) and then let it sit some more before wiping it all off with a damp cloth and rinsing well. If a single wash won't do it then a few washes over time should. Then there's always TSP for those who want the cleanup responsibilities.