dry it out. when you try to treat it inside the tank, you never know what could have happen. also this thing spreads fast so it's best to get rid of the cause as oppose to the symptom. if i were you, i would take out the whole tank worth of rock, dry out, vinegar bath, the whole nine yard.
i have seen them taking over the whole tank within months in one of my local reefer's tank and it's not a pretty sight. once it settles it's really hard to get rid of it completely without tearing the tank apart. so i would start by taking immediate action by drying them out and vinegar bath them. the longer you wait, the more agony you're accumulating for later on down the road.