From Wikipedia: Aiptasia sp. are considered pests in the marine aquarium hobby, because they are stressful to coral around them, and occasionally even sting fish and desirable invertebrates. They are often accidentally imported along with live rock. Once present in the aquarium, the polyps are notoriously difficult to remove as attempts to remove often inadvertently create more, due to new polyps regenerating from remnants. Hobbyists commonly put Peppermint shrimp inside the aquarium to control Aiptasia populations, as the arthropods regularly prey on small cnidarian polyps. The nudibranch Berghia verrucicornis is considered one of the best predators for Aiptasia sp.
In our experience Peppermint Shrimps are the best and most economical predator of this nuisance hitchhiker
Berghia Nudibranches are very effective but also very expensive and will die off quickly if they don’t find their pray
Kalk Paste, Joes Juice, Aiptasia X and other products are available to aid the control of this anemone.