I bleached all my liverock for my new tank build recently. IMO bleach is more than enough to solve the problem.
Fill some buckets, put rocks in, fill it up with freshwater, and some bleach. let them sit for a couple days. dump out bleach water after a few days. fill back up with freshwater again, add some water conditioner, wait a couple days, do it again. took me about 6 days total
rock went into new tank on day 7.... fast forward a month my seahorses love the new setup! so yes the rock can be used and will not be harmful