Win the War Against Bathtub Mold
To prevent mold around the tub or shower, spray the wall with an antimicrobial treatment, then seal the grout with two coats of grout sealant to keep water from wicking in. If the mold is extensive and tiles come off, rebuild the wall with cement board tile backer and new tile. If the wall is sound but the mold stains won't go away, try regrouting. Scrape out the caulk and stained grout, spray the wall with antimicrobial treatment, regrout and caulk, and then coat the whole wall with grout sealant.