Why do my emerald crabs all die?

[FreeEnergyReefer]

I just purchased 2 from petco cause I seen them eating bubble algae. One only had 1 claw but it was the last 2 they had so I got em. 1 week later I find the one armed emerald dead in the rockwork. Chalked it up to maybe he wasnt in good health. Now 3 weeks after that I cant find the other one. Both of them were eating well. I feed like crazy. Is there some sort of predator that snuck in on my live rock or something ? What am I missing here? Parameters are: Alk-9.0
Calcium-483
Magnesium-1350
Nitrate-12
Phosphate- 0.04
PH- 8.1
Trace Elements I use the red sea kit and just dose once a week by hand. Iron is the only one that's always near 0 when i test. It's just such a pain in the butt to test and I dont wanna just guess dose it incase i do too much. I know I've been slacking on my trace but I'm getting the whole red sea kit dosers,colored lines and really pinning my trace elements down next weekend.

On a side note- after these two mysteriously died, I remembered the first emerald crab I had in the 75 2years ago also died after living for 1month. Sorry no pictures or video

 

[highest_tides]

I have 7 in my tank and they really are only seen at night. On that note, I wouldn't buy from petco in fear of a sick/unhealthy critter.

 

[FreeEnergyReefer]

Thanks. I usually dont but the closest descent lfs is an hour drive and I wasnt driving an hour for 2 crabs. No idea of what killed them?

 

[highest_tides]

Totally understandable.

 

[JayA]

Could be molting? and not dead... If you find a "dead" crab check out the shell to see if it is empty. Mine molt every few weeks or so, still scary every time. They typically disappear for a few days during/after a molt.

 

[FreeEnergyReefer]

Could be molting? and not dead... If you find a "dead" crab check out the shell to see if it is empty. Mine molt every few weeks or so, still scary every time. They typically disappear for a few days during/after a molt.

I know the difference between a molt and a dead crab. Can anyone answer any of my questions though? Could a emerald crab predator be in the tank? What am I missing?

 

[Uncle99]

Sure, another crab having lunch, quite possible.
I found one, 3 years later after setting up a system and that was only because I was moving the rock to an upgrade.

I don’t keep crabs myself in any system, this one must have come in on a rock maybe as a juvenile, over the years, mysterious losses, couldn’t figure it out.

Once all crabs removed, no longer having any issues.

Or maybe it’s found a really good hiding place!

 

[Stoney]

Do you have any hermit crabs or snails that you've had for awhile? If so I doubt you have a predator. I've had this same issue with emeralds. Thought it was a predator but I've got hermits and snails everywhere. Cant be water quality either since I've done a couple icp tests and have had a fire shrimp alive and well for about 3 years. Most of my emeralds disappear/die within a month or two. I've had a handful survive up to 6 months before dying, but it's rare. Seems like a relatively common issue. Sorry I cant give you a definitive answer, just letting you know it might not be an issue with your tank.

 

[FreeEnergyReefer]

Do you have any hermit crabs or snails that you've had for awhile? If so I doubt you have a predator. I've had this same issue with emeralds. Thought it was a predator but I've got hermits and snails everywhere. Cant be water quality either since I've done a couple icp tests and have had a fire shrimp alive and well for about 3 years. Most of my emeralds disappear/die within a month or two. I've had a handful survive up to 6 months before dying, but it's rare. Seems like a relatively common issue. Sorry I cant give you a definitive answer, just letting you know it might not be an issue with your tank.

Thankyou soo much! I kinda figured it out. The 2 crabs I purchased from petco didnt make it but last night I scoured the tank with a flashlight and found 1 emerald crab and he's big n healthy. So,that being said I credit the other losses to where i purchased the crabs and them not being in good shape when i got them. I remember i bought 1 from a reefer friend and lost him soon after so i thought he died with the other 3 or 4. But no hes been alive this whole time tearing the bubble algae up. I've almost got it beat. Now I can focuse on getting rid of the random aptasia dropped 7 berghia in a month ago and I can already see a big if decline 3 even made it down the overflow and into the sump crazy. Thanks for everything I can finally purchas the last emerald for this tank from a good source,since I know they're surviving now. Happy Days