Another good article on using Fenbendazole for Eliminating Hydroids.
With good picture details on how the process works.
https://maxdraco.wordpress.com/2013/...-hydriods-etc/
After reviewing this I'm pretty convinced, I'll be treating the hydroid rocks by removing them and treating in my Quarantine Tank.
** THIS TREATMENT APPEARS TO BE Quite Harmful (other reading "google Panacur"). Stays in Live Rock and will harm Snails that graze on the live rock, will wipe out biodiversity in a DT. Unknown coral damage, etc **
I should be able to remove most of nasty hydroid rocks from the DT and just treat those.
Then consider future treatments as needed.