I like what Coelli said.....blowtorch the rock! But yes....aiptasia are a pain in the buttocks! It's hard to tell from the pic but if its an easy rock to pull out. Pull it out and let it sit in the sun for a few days. No harm in killing any bacteria since the tank is still in its cycle mode. Once cycled as others have said add a couple peppermint shrimp as a precaution to any aiptasia you may not see.