alright, i helped Tboy out setting up this tank, and normally i would tend to think of mantiss too.....
but heres the thing. some of the live rock was transfered from his well established tank, then he got a bunch of live rock from some dude. now the new live rock from this dude, sat in a 55g rubbermaid garbage can for weeks...the levels got out of wack,mag drive pump burnt out in the can, etc, etc.a real horror story with the rock in the garbage can...so when the rock went into the tank, massive die off and basically cleaned to all hell and tossed in to cycle the tank...
so if it was a mantis, wouldnt it show up in the last tank, and if it did hitch hick from this dude, wouldnt the reoccuring problems in the trash can, then cycleing the tank kill this possible mantis...
sorry for the strong contradicting to the mantis theory, but i am close the situation and find it hard for the mantis theory to be a real possibility....