vanishing peppermints

So i have not been able to successfully keep peppermints as they seem to disappear over night. what should i be looking for as far as predators go?

list of fish and known inverts:

damsel
hipo tang
3 ocellarious(spelling)clowns
6 line wrasse
spiny urchin
assorted hermits
assorted snails and conchs
and a couple emeralds

any of these that could be killing them off??

i have introduced a total of 8 over the last year and have yet to ever see one. is that normal??

I agree with jwoo, shrimp are very sensitive to changes in water chemistry, but that said peppermints are also nocturnal. Try scoping your tank out a couple hours after the lights go out and you may see them.

There is so much you can see at night. Everything that isn't out during the day comes out at night. Wait at least 1/2 hour after lights out. A dim flashlight is great for viewing after your eyes become accustomed to the dark.