Disappearing fish.

[Canadoc]

Hello all,

So... I have a 29 gallon tank, assortment of Zoos and LPS corals. I've had fish randomly dissapear over the last 1.5 yrs... and it's really beginning to irk me. So far have lost a firefish blenny, a lawnmower blenny, and one clown (he just died though... about 3 yrs old.... poor guy). The other two I never saw again. Shrimp don't seem to last long either.

I know the usual suspect is a Mantis.... but I have never seen one, never heard one, have put out traps... and nothing.
I do have some biggish emerald crabs.... could they do it? Rawr. I miss my fish!