Mass Scarlet Carnage

[ncsnake]

Put a clean up crew in my 60 gallon 2 days ago including 20 scarlet crabs. Came home today and there are dead crabs everywhere! In a few cases their limbs are laying around in the tank...others are intact but deceased. I found a few alive but they don't appear healthy.
Peppermint shrimp,emerald crabs and snails added at same time seem to be fine...other tank inhabitants are 2 small percs and 1 blue damsel.
RO water is Nitrite 0, Nitrate 5, Ammonia 0, salinity 35ppt, Temp 80.0 and PH was around 8.6 after lights had been on about 4 hours.
Why did my crabs croak?

 

[moopiespoo]

Are you sure that they didn't just molt?

 

[ncsnake]

Dont think they molted because they are dead in their shells.
They were all very active as late as 9:00 pm yesterday and now they are all dead.

 

[saltwatervirgin]

I was told that the pH of my tank should not be over 8.4. Mine usually runs right at 8.1 during the lighting ours. Maybe the high pH did it. Just a guess.

 

[moopiespoo]

Being that only these crabs died, and everything else is fine, maybe you just got a bad batch of crabs. The Ph is a little high but I wouldn't think that would kill all of them that fast. Besides your remaing crabs how do the fish look.? SWimming well, eating clear eyes?

 

[the claw]

Maybe the damsel is eating better than the rest of us....
Did you acclimate them correctly when you added them to your tank?
Do you have a test for copper? Copper in your tank will kill them first. Your emerald will be next. Do you use RO/DI water or tap? (There can be enough copper from your pipes in your house to kill) Is this an old tank or a new one. (residual copper from old tank can be high enough to kill.)

 

[bheron]

NC Snake-
I went through something similar, on a smaller scale, with snails. My first two guess would be:
1) The PH might be high - mine was 8.6 when my snails and other small inverts i put in literally liquified!
2) Echo the above - if you used tap water ,at all, and there is even ther slightest trace of copper in there, your inverts are done dude! That's what did my tank in.