Which clean up crew? Please help

wow that is one nasty hermit crab - what kind is it? I have only seen it happen early in my reef. mostly due to little amount of food and or not the right shell.

I have never seen a red hermit kill a snail - but like every creature they don't don't always follow the rules

 

What one must consider is that hermits, and most other crabs are OPPORTUNISTIC OMNIVORES, which means they won't pass up an easy meal. Once some hermits get a taste for snail flesh, they will ALWAYS eat snails when they find them. This happens more often if you overtock them, as they all compete for the same food.

If you want the "safest" hermit, stick with scarlet reef hermits (Paguristes cadenati), which are the red crabs with bright yellow eyestalks. We use these crabs

To be honest, and especially for a new tank, as a new tank simply can't support a large number of them...the same is true with snails. I wouldn't stock more than 10-20 scarlets to start in a 210 gal. Start small, and as your tank matures, you'll see which critters it requires based on the type of algae growth you have, detritus levels, and uneaten food amounts, and you can add more of what's working well for you.

I really don't recommend getting a package deal, as you generally end up with WAY too many critters, and they'll end up dying back to the level you tank can support anyhow. IMHO, it's best to build UP (and it's cheaper too!).

Here's a good CUC primer:

CHOOSING COMMON CUC CRITTERS

HTH