Thank you...Guy's really? Please do use caustic acid...this is a bad move, King of pain, stop giving brute tactic advise with zero sound marine biology experience. Dr. MegnaAcid will melt of the outer layer of the rock where all the Phosphates are hiding. I would clean them manually, than I would soak them in an R/O bath to pull out the phosphates. I wouldn't just throw them in your tank because you will surly have an algae problem for awhile until the phosphates are all gone.