They don't touch the guppies or feeder fishes
I think coz they are too small or coz the feeders tend to hide
on top
I'm thinking of buying cheap angelfishes and tiger barbs
I was complaining to a fellow hobbyist about them eating
everything and he said 2 of his Gulpers just ate up 4 of his Sea
Bass -_-"
ahh.. ohh.. i remember my friend's bloody luohan in the office..
whatever we put inside gets eaten.. top or bottom 
then we tied a plastic basket in the tank so that we put in the
guppies in the basket...
if the guppies were dumb enough to swim out, they get eaten...
if they don't they're safe...
the luohan just kept vigil there, waiting for the fish to swim
out...
overnight, all the guppies were eaten 