Peppermint shrimp will work, but you cannot feed anything else to the tank. if you are adding any other food for fish, they would rather eat that then aiptasia. I also think you could use more peppermint shrimp, because unlike some of the other species mentioned, they aren't picky eaters and they can survive off many types of food once the aptasia is gone.
I also have the "zapper" if you hear people mention that, this isn't the laser one, but the voltage one, and so far, I have not been impressed. I have tried it on multiple aptasia, and the ones that are in any type of crevice seem to be able to get away from the voltage enough to not be killed. Considering I have very porous rock, they are usually able to get away.