As you might know i have had trouble with my fish going missing!I give thanks to the people who gave advice on what to do for this case !I think for sure that I do have mantis shrimp in the tank!I have been to my local aqarium shop where there is a resident marine biologist who has GIVEN me a halfmoon triggerfish to try and ambush the culprit!!!!!I will keep you posted on any developements!!!!!