Why can't I keep emeralds??


Hi again!
Has anyone else here had difficulty keeping those Green Mithrax Emerald Crabs??
Mine NEVER last more than a month!
I feed them Nori regularly, and here are my water parameters:
pH = 8.3
Alk = 10 dKH
NitRITES = none detected
Ammonia = none detected
NitrATES = 20 ppm (could THIS be the problem??) I dose with vinegar.
Phosphates = .10 ppm

Really weird because all my fish are doing great, as well as my snails, 2 urchins, 2 shrimp, and I have SEVERAL hermits. All of those are also ok.
Really unfortunate because I really like the emeralds but I'm reluctant to add any more until I find out the root cause of this problem. Or are they just too plain hard to keep for most aquarists??

Any insight from anyone would be appreciated.


Premium Member
There's probably more than one reason. Two come to mind. First is stress from shipping and handling, especially if they are all from the same source. Second is predation, they are pretty safe most of the time but when they molt they are very vulnerable, it's possible one of your current livestock recognizes it and kills them when they molt.


Super Best Friends!
Premium Member
Don't lose too much sleep over it. I've never been able to keep them in my tanks without issue. In fact, I don't keep any crabs in my tanks for the same reason. After a while, they seem to get bored with the normal "crab fare" and go after coral. They usually pick on LPS corals, but I've seen them bother a softie on an occasion or two. Chalice, favia, favites, and acans are the biggest risks in my experience. Maybe it doesn't happen in larger tanks, but I've seen it in 40g and less. I never added crabs to my 120, so I can't comment.

BTW, I've seen peppermint shrimp do the same thing. Coral aren't their normal diet, but they seem to adapt.


New member
I went through 3 emeralds before one stuck. Idk could be the stress from transport someone mentioned.

Also, I would go for weeks thinking that the last one was a gone but then it would come out randomly at night. If you haven't seen yours in a couple of weeks it could be that it's hiding.

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New member
Had one just die myself. Made it a few months. Eat like crazy though. While they are fascinating, I'm not certain I've had one for more than a few months. I had to relocate a smaller polyp zoa as one night he are all but 1. Finally have 4 heads 2 months later. Never seemed to touch anything else (that I'm aware of). Cool crabs [emoji886] buy I haven't cracked the secret to keeping them myself. Hoping you have better luck with next one.