Crab only cleanup crew?

[Seamonkey]

I don't have much luck with snails either. I buy 5 and within 2 months there is usually only 1-2 left. I think they are turbo, anyway they are the ones commonly seen in the LFS. I have only 1 hermit crab in my tank, he's not really big, but I often wonder if the's the culprit making the snails disappear. Anyway, in my 20 gal. he seems to do a pretty good job of keeping it clean, other than the glass, which I scrape with a blade.