I have a 55g tank in my basement that has a bunch live rock, a few zoas and a blue damsel in it. A few pieces of live rock have small hydroid colonies that I've let grow so I can test different treatments on. They are a colonial type that don't spread very fast and I've tried a number of different treatments that I end up using in my display tank if they're effective. Now I'm at the point where I want to get rid of them all together. If I take the live rock out and nuke it can the hydroids survive in the substrate? I can break the tank down entirely but I'd rather just eradicate the rocks and leave the rest of the tank running. I've never seen any hydroids growing on the sand but I'd hate to kill them off on the rock only to have them come back because I didn't do the whole tank.
