Crab Molting Issues

In the last month I have lost 2 crabs and am not sure why.

1 month ago
The first one was an Anemonie Crab (the filter feeder type) and it started to look brown instead of white, so I expected it to molt soon. The next day I found an empty shell of a crab and assumed that the crab had molted. Not so, never saw the crab again.

2 weeks ago
The second one was a green emerald crab. The crab started looking white (I assumed corline alga was growing on it) and it had lost a couple of legs. I assumed once again that it would molt in the near future. One day I came in and there was an empty Husk of a crab -- still very intact but definatly empty, but I have not seen the emerald since.

Also it seems I have significant less Hermits since I set up the tank last October.

Any ideas what the problem might be?

Tank inhabitants
-- Cleaner shrimp
-- Pearly jawfish
-- Royal Gramma
-- White Barred convict Goby
-- snails
-- hermits (blue leg, grey leg)

Its only a 25 gallon so if I had something like a mantis I am sure I would have heard or seen it by now. (Plus I doubt the left over crabs would have been intact.)

Edited by Kevin - May 06 2008 at 5:22pm

I don't know the Alt and Ca levels. Last time I tested alk it was around 2 meg per liter. Calcium, my test kit was bad so I was getting bad readings. The fish store said around 440. It has been a while since I have tested so I will test again.

One note though -- My sps corals are growing very well. (All except a pink stylophora that just finished dying.)