i use a scoop of vanish oxyaction crystal white in every whites wash i do, and have really noticed a difference in the 9 or so months i've been using it. i only ever wash at 30 too. if your whites are badly yellowed/grey it may take a few washes to bring them up sparkling, but it's worth it. if they're small stains i'd give them a squirt with a pre wash first. you just have to keep at it.