My problem also is aiptasia. If this does not kill the aiptasia, there will be some left hiding in small crevasses or tiny holes in the rock. There would be no way to scape off every last one. Leave one on there and they will start to multiply as soon as you put the rock back into a tank with light.
Any that you find you can smother with Aiptasia-X or Aiptasia Rx. It's easier to work on them away from the aquarium. They are annoying, but won't end a reef unless the owner never intercedes. Part of good husbandry is dealing with stuff like this when the issue is minor.