It looks like you already have an answer, but in case you wanted other options, hydrogen peroxide helps. Just bathe the rock in a bowl of hydrogen peroxide (enough so that it bubbles within seconds of you adding the rock), and leave it in there about 3 minutes. Bacteria should have enough protective enzymes like catalase and peroxidase to survive that short of an exposure but more macroscopic organisms like flatworms and macroalgae will die off. It wiped out my hair algae problem out though I should mention that for about a week it looks like you did nothing, but after that, the hair algae ( if you have it) will turn a light green and sluff off. I didn't mention it, but a rinse step is necessary especially if you have a small tank, don't want that peroxide in your tank! Hope that helps . Almost forgot, zoas/palys and mushrooms can survive the dip as well, but was too chicken to try it on any sort of stony coral.