Hey GQ,
Few days ago, I bought 3 yellow tail damsel. Two of which were browsing around, nipping at my liverock (at that time I only had a 11 lbs chunck of fiji), as well as eating my food and stuff. However, one just went into hiding (although I could see her).
All were good until one simply vanished!
I looked everywhere, but she was gone from the the face of this earth! I thought it was Mantis Shrimp and kept the Liverock out for 10-20 minutes, but a spyder crab came out only. Then, I notice that both of my fishes were all scared...hiding whenever they see me. Probably hates me for stressing them out (a little)when I took the liverock out and looked for the other fish.
Then suddenly, 2nd one died (this time I saw his deadbody (and my "NH3 /NH4+" had a hike) but PH was at 8.5, Nitrite less than 1.5mg/l.
I thought 1)could be stress 2)could be already sick
long story short, I changed partial water and decided not to get anymore damsel during cycling. Liverock should be doing the job for me.
Oh yeah, for 2 days, I don't see my 3rd buddy anywhere (Now, liverock is 50+ lbs, so not interested getting all out). May be I starting cycling again with new addition of liverock and he couldn't take that amonia hike)...but who is eating them?
Moral of my story, if they are stressed out...could be bad water condition, a deadly creature scaring 'em or simply you got sick fish!