I have searched the inter-web dry and I have yet to find a solution for Colonial Hydroids. I have boiled, burned, baked, dried, juiced, smothered and plucked these little buggers. For every 1 I kill 3 come back in it's place. While my fish are in the hospital tank, I am thinking about fragging my corals and removing my live rock and starting again. However, with ICH it has a period in which the spores are alive in the water column. Do hydroids have the same thing? I would hate to get fresh 200 lbs of live rock only to have them pick up the hydroids again. Do I need to dump my sand too?