hermit crab death

[dan-in-den]

During the night, it appears that I lost 3 or 4 hermit crabs and another one died today. I pulled out the bodies of the ones that died during the night (they were out of their shell and mostly eaten) but left the latest casualty in the tank, still in the shell.
Only changes over the past few days is that I'm trying a home brew food (pulverized concoction of octopus/squid/shrimp/mussel/Formula 1 flake/frozen spirulina formula/garlic frozen in saltwater from tank) and I'm slowly raising the Ca level with Kent Turbo-Calcium (shooting for an increase of 20ppm/day with a target of 400+)
Two questions:
1. Should I just automatically remove anything dead or leave it for the scavenger crew? I've got a peppermint shrimp that is doing his best to pull the crab out of its shell but not having much luck yet.
2. At what level does nitrate become dangerous for inverts/fish? I had a spike over the past few days but it is on it's way down. Peaked at 5 mg/l yesterday but is down to 4 today. I'm pretty sure that it was caused by overfeeding (not sure how much of my home brew to feed yet)
Current readings:
Ammonia = 0
Nitrite = 0
Nitrate = 4
Ca = 385
Alk = 4.65
PH = 8.2
Temp = 79
Livestock (125g)
6 green chromis
1 black cap basslet
2 neon blue goby
2 peppermint shrimp (was 3. 1 died over the past few days or molted and is hiding)
30-40 hermits (red/blue/mutts)
30-40 snails (turbo/astaea)
130 LR
sand substrate
Thanks,

 

[dan-in-den]

in fact, you might be able to see the peppermint shrimp working on the dead crab by going to http://danindenver.ontvnow.com
The lights on the tank are on from roughly 8am to 8pm MST

 

[007]

perhaps your hermits just molted. The remains of a molt look very much like a partially eaten carcass. Its a common occurence when crabs and shrimp are recently acclimated to a new system.
For small animals that die such as hermits and snails, i just leave them for the clean up crew. But for larger things such as a coral or fish, I remove them as soon as possible. The larger animals release a significantly greater amount of ammonia and nitrogen into the system.
As for nitrates . . . well you are going to get mixed responses on this, but I dont think that nitrates will be able to accumulate to toxic levels in a properly set up marine tank. Nitrates get consumed/used by one of several methods that one of which will be present in a marine tank.
1. A DSB will effectively prevent nitrate from reaching toxic levels through the function of anaerobic bacteria.
2. Macro alagae will also consume nitrates preventing them from being a problem.
3. Micro algae will develop in a system where there is an excess of nutrients. This is by no means a desireable export method, but it will prevent nitrates from becoming toxic.
4. Water changes that are done regularly and in proper proportion will also prevent nitrates from becoming toxic.
It is my understanding that fish can tolerate rather high levels of nitrates. I have heard 100+ even although I question the validity of this claim. Invertebrates . . . I have no idea, but I would assume that it is considerably lower. While 20ppm is definitely an undesirable level, I don't think that it would hurt anything except cause an algae bloom.

 

[dan-in-den]

Thanks for the info. The one in the shell is definitely dead and the others may have been molts. My peppermint shrimp keep trying to pull it out but haven't had any luck yet. It's fun to watch them.
My tank is still immature (about 2 months old) and I don't have my lighting built yet so I'm just running off about 60 watts of NO at the moment.
One thing that I don't have is a copper test kit and the water that I'm using is deep aquifer water that has been tested at <.05 mg/L (copper) by the Health Dept. Does copper accumulate? I assume regular water changes keep the level down.