Wrasse Death

[-Nemo-]

This morning I found my six-line wrasse dead who i've had for a little over a week now. I had a feeling last night, that he wasn't going to make it as he didn't look good and wasn't acting like his self. Last night I noticed his poo was white and stringy which is certainly a sign of illness, especially when it was feeding time and the usual greedy wrasse wasn't eating. His mouth was also wide open, and he wasn't swimming around hunting for bugs like usual, but rather swimming against the powerhead current in one spot. Then right before the lights went out, he settled down between two small pieces of LR and wouldn't move. That made me nearly positive that he hasn't going to make it through the night.
Unfortunately, even if i knew what was wrong with him, it was too late at night to do anything about it. Just that morning he was perfectly fine. Anyone have any clue what happened? Tested all my levels, they are perfect, the other fish are fine, and so are the coral.
I'm planning on getting another one shortly, and would like to know what happened to this one.

 

[SkiFletch]

Internal parasite or Cyanide poisoning during capture are my only guesses.