An Easy, Home-Made Natural Grout Cleaner – Hydrogen Peroxide.
Use half a cup of Hydrogen Peroxide mixed with one cup of water. Put it in a spray bottle and spray it on the moldy areas.
Let it sit for a few minutes and then clean the tile grout with a toothbrush. Toothbrushes will not mar tile surfaces. It shouldn’t really need too much scrubbing, you are really just working the peroxide into the surface. When you clean it off, you should scrub over it again to remove anything that has loosened. Rinse with clean water.
Spraying the grout with peroxide on a regular basis will also inhibit the mold from forming soconsider keeping the bottle in your shower and spraying everything down periodically.
This natural method is fairly simple and cheap but it does work.