Strange fish problems

OK so this is just strange.
I've lost my Manderine Dragonett. He was just over 2 years old and eating Mysis every day.
Then today I find one of my 3 year old Chromis has been in a scrap. It's dorsal fin is chewed up and has several laceration on it's body. It's still eating and very active but man what the heck is going on.

I don't really have anything in the tank that would cause such damage to the Chromis. Other fish include; Chevron Tang, Bi coloured Blenny, 2 other Chromis
Inverts include hermits and snails, Linkia Star and a hitch hiker long spine urchant.

Anyway will watch everyone else to mack sure the chromis doesn't have a parasite

J

 

my dragonet is also missing along with three other fish one has disappeared every fourth night for a couple of weeks. I think it might be aliens, or something like that, strange thing is no bodies

 

My wife won't let me put anything new in the tank until I find the culprit and she is not buying the alien thing
Have you gotten any live rock lately

 

No, no new Rock. My ammonia is zero even today

J

 

Jason, don't you have that big unidentified crab? Or am I thinking of someone else....

 

When my tank crashed I had a bunch of coral over at a buddies house.
Needless to say he has a big scarry crab in his tank now

J

 

Dude!

 

That's such a beautiful fish! And after two years...
You must feel terrible. I hope you find out what caused this and are able to fix the problem.

Jim