mysterious deaths

[daisy]

In my 55 gal there is cc, rock work, three powerheads, a protein skimmer and an emperor double-biowheel system. There were four turbos, two hermits, one sally lightfoot, a maroon clown and a sailfin tang who has been suffering from HLLE for over a year. I have plenty of critters in the cc (worms, mostly). The PH, ammonia and nitrites were all very good, and I was working to get the nitrates under control, though they were reading under 40 ppm (just). This morning I found the sally dead on the highest rock in the tank, just out in the open. Also, I think I've lost two snails, though I'm not sure yet. And the fish are not acting as "well" as usual -- instead of swimming around the open spaces, they're hiding, though they did eat a little this morning. The only changes recently have been more frequent, smaller water changes and the temp has been a little higher due to the warm snap we're having here in NYC. I'll be checking my chem levels soon. Any other ideas? Any chance the sally starved? I've had her for over a year, and I'm really sad I lost her. Please help!
thanks.

 

[daisy]

Okay, you were right. She just molted. The thing is that I was so convinced it was really the crab -- there was connective tissue, and eyeballs and everything. This happened once before, that I thought she was dead and it was just another molt. I feel like an idiot.
I have changed to smaller, more frequent water changes in order to try to kick the nitrate problem. So far, though, no change. Suggestions?
I filter my tap water through a resin that removes all the metals and supposedly everything that you don't want in your tank. I forget who makes it -- something or other pharmaceuticals?