Ways to kill aptasia anemones:
1) Use a syringe full of very hot water to literally "fry" the anemone
2) Use a syringe full of calcium additive to poison it
3) Get a red-hot screwdriver (with a plastic or rubber handle) and shove it into the anemone's hiding place
4) Attempt to remove the rock or bit of gravel it's attached to
5) Get a machine gun, a large axe, a flamethrower, a carpet, and either a sledgehammer or a large rubber mallet. Chop the tank apart, spray the anemone's area with bullets from the machine gun until the gun is emptied, pound the area into the basement with the mallet or sledgehammer, fry the entire area with the flamethrower, and then put the rug over the mess whenever your mother-in-law comes to visit.