Ive read a lot articles (back in my freaking out over palytoxin days) that state only bleach will neutralize the palytoxins and is what is used when doing a detox accident. If memory serves me the ratio was 20% min bleach and 80% water. If it was me id use a bit more probably a 30/70 blend & let it sit in a safe area outside for several days with a tight lid then a cold water rinse off & a soak in plain water for a while until all bleach odor is gone if the rock is really that important or unusual in shape and worth the trouble and possible sickness. If it was in my tank which will never ever happen id put it very carefully in a5 gal. bucket with above stated mix & a screw on lid, let it sit a few days then pour out the water, re-seal & toss it ............ if no one wants that nightmare.