Why are my crabs dying?

Hi everyone.

I don't understand why, but it seems as though my crabs aren't surviving my 3 month old tank.

I have had 3 crabs die in the past 4 days.

I know copper is the first red flag, but i have poly filter installed, so it can't be that.

Calcium is at 440ish? I'll check it again in a few to make absolutely sure.

Nitrites 0
Nitrates are a little high, maybe 20
Ammonia 0
pH 8.3
Salinity is 1.024
temp 79

Tons of algae to eat, and I feed the fish once a day, so they have plenty to eat.

My snails are thriving and eating more than ever.
I had an emerald crab looking awesome, then dead the next day. No slow deterioration or decrease in activity.

Any ideas?

 

I wish I had your problem of only crabs mysteriously dying off.

Are you sure they're not just molting, and you're thinking the molt is the crab? It's happened to me a whole lot; my big hermit molted, and it looked like a whole body, but I saw it walking around 3 days later.

 

Hmmm that's weird. Are you sure that they are not molting. Did you checked the crab to see if there are any damage of some sort?

 

+1 probably just molting

 

Ok - so one of them was molting.

BUT

Two of them are dead. One was an emerald crab, and he pretty much disintigrated when i picked him up (and it wasn't a molt. he's dead for sure.)

The other one was a hermit, and he is definitely dead.

I'm not sure what to think.

 

stray voltage? do you have a grounding probe?

 

I'll look into it, but I highly doubt it. Everything in this tank is less than 4 months old.

Can I just grab a multimeter from my dad's shop?

 

Yup, just ground one lead and stick the other in the water. Check for both AC and DC voltage.