Berghia Nudibranchs are a very effective predator of Aiptasia anemones. I have often described them as a wildfire. Adding a handful to a tank filled with Aiptasia at first may seem fruitless but once the nudibranchs begin breeding and laying eggs they quickly consume all the anemones in sight.
Berghia unfortunately are an obligate carnivore of Aiptasia so they will starve out slowly after consuming all the anemones. They are also the favorite food of some varieties of wrasses so sometimes their tank mates eat them before they are able to address the anemone issue.