What is eating/killing our fish?

[Dreamreefer]

Hi. We have a 75 gal. reef tank. Currently we have 2 clown fish, 1 cromus, 1 watchman goby, and 1 tiger shrimp (who lives in the same burrow with the goby.) About 6 months ago, we lost a few fish ( 1 corral beauty, 1 yellow tang) over a week or so. They had been long-time residents. We noticed they had been nipped a lot on their tails a few days before they disappeared.
So 6 weeks ago, we added a royal gramma, and another corral beauty, both full grown and big. Just a few weeks ago we noticed the corral beauty had a nipped tail, and then it disappeared. They had been eating well and doing fine. Same thing with the gramma, only we did find part of it. Our water is ideal, tank sparkly and beautiful.
A year ago or so, we killed a smallish (2" diameter) rock crab.
Do tiger shrimp nab fish? We have checked out the tank at night under it's moom lights, and haven't seen anything. The fish hang out behind the rocks at night- is it possible something just hangs out back there?
Any suggestions are welcome. Thank you so much!

 

[mmkeeper]

Hitchhiker crabs, brittle stars, carpet anemones, to start.

 

[Jan]

mantis shrimp...


Do you ever hear a clicking sound coming from the tank?

I even had a coral banded shrimp that took out a couple of fish.

 

[120gallons]

Any of the fish agressive towards the others, could be dying of stress, etc. It's amazing how fast a dead fish can be completely gone in a tank....less than 24 hrs.

 

[LarryB]

maybe the clowns are thinking about spawning and are getting territorial?