Maybe you got camel shrimp instead of peppermint shrimp? I know that a lot of LFS here don't know the difference and will sell camels as peps, although I don't know if the camels are more predatory than the peps. I have heard that the peps will take down polyps, but don't know firsthand if that happens. If you get rid of your peps, would you by any chance want to trade them for some xenia? I've been looking for a couple of peps to kill off the small amount of aiptasia I have in my refugium, and also take down a couple of aiptasia in my reef, and haven't seen them lately (except at one store that wanted $39 for them, not a chance on that sale going through!).