Joe's Juice, vinegar, kalkwasser, lemon juice, peppermint shrimp, boiling water in a turkey baster, Cobberband Butterflies are a number of ways to rid your tank of these pests. Be careful if you try to pluck them out. They can spread more. One other way is with a torch. If they attached to a rock, take the rock out and give them a quick shot with a torch. Good luck.