emerald crab death

[zaphod42]

Hi. We got our 1st emerald crab on March 12, for a gha/turf algae problem. We also got some trochus and a fighting conch at the same time to beef up the cuc. And a brittle star for enjoyment. Everyone was doing great for 10 days, except I haven't seen the conch since he dug himself into the sand bed. I assume he's under there somewhere. The emerald crab- Lefty- was going to town on the algae for a while. But Tuesday, Mar 24, he suddenly stopped eating. Wednesday he was upside down on the sand, and by yesterday (Saturday) he was dead. Definitely not a molt, but the entire crab.
From my older group- everyone who's been in there for 1 to 3 years, they're all doing well, except for a banggai cardinalfish, which suddenly seems bloated. This may be because I was examining everyone so closely to see if anyone else was effected. The cardinalfish is now in QT.

But my question for this forum is, is there any reason for this death that I am missing or should watch out for?

Tank is a 40g breeder, about 3 years old.
Equipment:
Added a small hob refugium about a month ago with chaeto.
Hob tidal filter with carbon, gfo, and filter floss.
Small hob protein skimmer.

Livestock (before Mar 12):
2 clowns
1 damsel
the aformentioned banggai
3 anemones
1 pistol shrimp
about half a dozen blue legged hermits
maybe half a dozen ceriths
some corals

Parameters:
salinty 1.0256-8 (tropic marin hydrometer)
nitrates 1 to 2 (salifert)
phosphate 0.15 (hanna)
ph 8- 8.15 (salifert)
Alkalinity 10.5 (salifert)
calcium 430 (salifert)
magnesium 1200 (salifert)

thanks for any input or advice!

 

[ColorMeGone]

I had one for months along with two pithos and once all the algae was eliminated I would feed them all nori everyday. He crapped out but my two lazy pithos are still waiting for me to feed them everyday. lol
Just happens I guess?

 

[Boehmtown]

I can tell you 2 things. Sometimes they've already been damaged/starved from shipping etc and it's just a matter of time. And pistol shrimp could have rocked it, or the clowns , Especially if it had a fresh molt and was still soft. They have wildly different personalities, which give them wildly different heartiness. Just get another. They are mostly food in the ocean, so some are not great at surviving