the immediate area, and it is more effective to actually get a syringe like a diabetic would use and physically inject the boiling water into the mouth of the anemone, also kalwasser mixed quite thick does the trick even better, turn off your filtration and water movement, inject the anemone, and then coat the surronding area to ensure that you have killed it, i am told that they reproduce not only through the water column, but the base actually buds off and forms many new anemones that you may not be able to see when they are small and still near the parent anemone, that is why i say to coat the area around it as well, about the size of a quarter is the area i cover, and i havent had an aptasia in years because of this method.