Could a crab eat my fish?

The only crabs I have in my tank are a couple of emerald's for bubble algae control (largely ineffective, btw) and a few tiny scarlet reef hermits. IME, the scarlet reef hermits are the only ones that won't eventually bother something they aren't supposed to.

x2, the scarlet hermit is the ONLY crab I will allow in my tank. My emerald green crab is living in the sump and is now HUGE. He killed and ate one and was eating the other royal grammas so it earned him life in the sump. He's slowly killing the blue legged hermits that I banned to the sump too.
 
I'm in agreement with one of the previous responses , when there is something dead in the tank everyone comes out to party , meaning all the creepy crawlies we don't see at night .
 
There are clean up crew that can be effective. Nassarius Snails are my personal favorite snails. They hide in the sand for the most part and come out to eat meaty foods. They do a great job keeping the sand clean too. I usually have a mix of Trochus and Cerith snails too. They usually do a good job cleaning a variety of algae. I also have a pencil urchin (which you have to be careful with if you have coral) who does a great job with algae as well. My final, and one of my favorite for looks, a Cowry, but I'm not sure what algaes he targets, only that he is always crawling all over the place. Mine was sold to me as a \Money Cowry, but I'm not 100% sure that he is. He hasn't touched any coral like some will, so I'm happy with him. And he's really cool looking. I do have two Blue Leg Hermits, but that's only because they are the only ones I haven't got rid of yet. I don't like them because they kill snails, but mine have been good for awhile now. The Ceriths are too small, and the Trochus I think are too fast/strong/undesirable shelled. I also hear alot of people suggesting Turbo for algae, but I've never had luck keeping any alive, even when I had a ton of hair algae.
 
I'm sure the scarlet reefs are fine. But I probably have 15 of them in my little tank and they never touch any algae. They're always right on top of my corals picking stuff. They don't seem to do any real harm. But they don't do any good either.

I'm on team husbandry. I can keep my tank clean. I'm obsessed enough that if there is something that needs taken care of, then I will take care of it.

How likely are the Cowry snails to mess with corals? Because they are cool.
 
I'm sure the scarlet reefs are fine. But I probably have 15 of them in my little tank and they never touch any algae. They're always right on top of my corals picking stuff. They don't seem to do any real harm. But they don't do any good either.

I'm on team husbandry. I can keep my tank clean. I'm obsessed enough that if there is something that needs taken care of, then I will take care of it.

How likely are the Cowry snails to mess with corals? Because they are cool.

Be careful, some species are coral eaters.
 
If the cowry snails are going to be bad news I'll just let it be. I'm learning quickly to pry myself away from something that is going to be trouble no matter how beautiful it is.
 
The Money Cowries are supposed to be reef safe. Mine has not touched any of the corals, but I'm 99.9% sure it's not a money cowrie. I'm not 100% sure what it is, but it's bigger than money cowries are supposed to be and way cooler looking than money cowries.
 
I don't have a picture, but my best guess is that it is a Snakehead Cowrie which are supposed to be reef safe.
 
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We bought an existing 180. Few months in we started having irregular fish disappearances. Finally shut down the tank and removed every rock. Found a rock crab hidden up in one of the rocks. Introduced him to the sump and have not had any fish disappearances since.
 
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