Cucumber maybe? As for snails .... my fighting conch is the one I see do the most sand cleaning .... but supposedly the cerith and nassarius will also eat detritus.
Will your frag tank have a sandy bottom or be bare bottom? If a sand bed, I'd suggest Nassarius Snails. If bare bottom, just siphon off detritus, on a regular basis, or position a power head low, to keep detritus suspended.
I have a problem with it in my 'fuge. It seems like my pods like to eat the stuff, though I did had to siphon off a good amount of it since I had a good 1/2" of it all over it.