it be caused by a couple things. direct current or too strong a current will cause them to bend over and not pulse. being so new to the tank, it could still be getting use to your water. it could using the energy usually used to pulse to do other things. it has been known that xenia does not ship very well, and may take a little while to take to your tank. also, xenia does not ned to pulse in order to survive, it is just kind of an extra benefit to the aquarist. sometimes they will just stop pulsing for no reason, then start again down the road. just be patient and see what happens, that is all you can really do.