Many would argue that the natural method is the way to go, but is not always as effective as the chemical method. The natural methods will add life to any coral reef aquarium including the future of accidental introduction from new coral additions.
There are three natural methods that i know of and probably the most known is the introduction of a true Pepper mint shrimp. My past experience has shown me that these shrimp don't tend to consume big Glass anemones, but certainly control and stop the formation and growth of new aiptasia.
The second method that i have no experience with are Berghia nudibranches.I have found out these will consume aiptasia, but that is all this type of nudibranch will consume, so after it as all gone the nudibranch will die. I have read that few shops will take these back off your hands after the glass anemone is consumed, The Nudibranch can then be resold. A great idea, but i guess stressful for the nudibranch.
The third method of control is the introduction of a copperband butterfly fish. These are just as effective but are not suitable for all reef aquarium. These fish grow quite big so a suitable size aquarium is required.
There is a off the shelf method of eliminating aiptasia called Aiptasia X .This product works really well and is really simple to use. The effects of this product is visible within 24hours. It is simple to use, just turn of any circulation pumps and inject the fluid into the centre of the anemone with the provided syringe. Wait fifteen minutes and turn on your power heads. The anemone will die off over the coming week. If any more appear in the future simply retreat as described.
To conclude If you don't have any aiptasia i would recommend the introduction of a Pepper mint shrimp for a small aquarium as a part of your clean up crew. If you have a large aquarium the introduction of a copper band butterfly fish would make a good addition to your fish collection. If you unlucky enough to be plagued by aiptasia i would treat with Aiptasia X.