We recommend using MoldStainKlear Interior.  After you spray let sit for approximately 5 minutes and scrub with brush. If it is heavy mold growth, rinse after brushing and then spray a final time and let air dry. Shower can be sprayed after each use for maintenance.  Keep in mind if the grout is damaged by the mold (actually has started consuming the surface) then the stain might not remove and may be necessary to replace the grout or cault for more permanent results.  We recommend keeping a spray bottle nearby and spraying after each shower.  Just spray and let dry.