say goodbye to aiptasia
The first thing you can do is limit the Aiptasia's chances to thrive. Target feed your fish and corals to avoid letting the Aiptasia steal any food. Although Aiptasia contain their own energy-forming zooxanthellae, feeding them additional nutrients won't help matters.
Next, develop a plan of attack. Many hobbyists attempt to remove Aiptasia physically, but that often creates only more polyps, and thus, more problems. A safer approach is to first invest in some natural Aiptasia predators.
natural aiptasia predators
Peppermint Shrimp (Lysmata wurdemanni) are a popular tool against Aiptasia. Make sure that you purchase the Lysmata wurdemanni and not its Pacific cousins, Lysmata Californica and Rhynchocinetes durbanensis, which are less interested in Aiptasia. Keep in mind that not all Peppermint Shrimp will be interested in the anemones, either.
Copperband Butterflyfish (Chelmon rostratus) is also helpful against Aiptasia, but may also pick on clams, sessile invertebrates, feather dusters, or other anemones in the aquarium. Research the recommended conditions for keeping the Copperband Butterflyfish and Peppermint Shrimp on LiveAquaria.com before adding to your aquarium.
Although difficult to find in the hobby or keep alive in an aquarium environment, the Berghia nudibranch (Berghia verrucicornis) is a proven consumer of Aiptasia. They are very small (10-14 mm), nocturnal, and can take months to develop into a successful Aiptasia-eating colony, but can reduce Aiptasia populations significantly or entirely over time.