I would keep the rock you have and use berghia nudibranchs in combination with a couple peppermint shrimp take the fish out and do not fee the shrimp for a couple days if they do not start to eat the aiptasia after 1 - 2 days. They will go nuts eating the aiptasia once they get the taste for them. when I put a new rock in my tank that has aiptasia they eat it over night never to be seen again, I only use peppermint shrimp. There is no use in boiling the rock and getting new stuff that would be a waist of your money that you have already spent..

Bill