problem with fish dying

[Puffer22]

we have a 56 gallon tank, lots of live rock and even some coral which is all doing fine. first fish were chromis... we got 4, one died after a few days. (by the way, tank was cycled and tests are done every few days.) we waited about a week between fish and got a royal gramma next, then last week we got a lawnmower blenny. all seemed to be going fine. complete tank list now:
3 chromis
1 cleaner shrimp
6 large snails (astrea i believe)
60-70 tiny snails
12 small blue leg hermits
1 emerald crab
1 lawnmower blenny

and now.. 1 dead gramma. all inhabitants are checked daily for any sign of disease and watched to make sure they are acting normally. everything was fine until yesterday. i came home from work in the afternoon and the gramma was hiding in a large cave. our shrimp had just molted and a huge molt was right in front of her (although she had another exit) while working to get ready to get that molt out of the way, the gramma dashed out the other exit and under a tiny burrow in the rock. she didn't come out for feeding time and weren't really too worried that we'd seen no sign of her. today i got up and examined the tank to find a dead gramma out in front of the cave it lived in, dull colored and mouth wide open. what would cause this? all readings are good. just bad luck?

[Andrew]

Please post the water levels....

[Puffer22]

i have to leave for work, but will have someone post them for me. if not, they'll be up tonight. and i just wanted to add... the gramma was very bright colored until i found her today.