what's eating my Acans

My acans seem to be fine one day and then I come back the next and half a polyp is missing. It is not a gradual thing. Here are the fish that I have in my aquarium.
-1 multi colored Fairy Wrasse
- 2 Ocellaris clownfish
- 1 starry blenny
- 1 disbar anthias
- 1 Yellow prawn goby
- 1 red starfish

Recent changes: I now have a media reactor and placed carbon and phosguard in it about 3 weeks ago it is running 24-7.

Yellow Tang recently died, it had been picking on the blenny, so now the blenny is free to roam more so than before.

My parameters are all within normal limits. Calcium might be a little high.

 

Blenny, goby and starfish could be culprits along with amphipods.

 

How long has the tank been up for ? Did you use live rock?

 

I've never heard of prawn (more commonly known as watchman's) gobies eating LPS, and IME amphipods will leave coral alone unless it is already dying or stressed.

That being I have to say the starfish would be the #1 candidate IMO. By "red Starfish" I assume you mean a red fromia? Typically in smaller tanks once they deplete their natural diet they go after things like coral.

 

the tank is 2 years old now. Never have actually seen the starfish on the rocks. It is not a red fromia starfish, at least going by pictures, but I unfortunately do not know what species it is.

 

going with starfish

 

Posting a picture of it would definitely help. IMO 65 gallons is still too small for most starfish, aside from the asterina genus. Also, you can't go by what you see; unless you watch the tank for 24 hours.

 

Agreed, a pic of the star would be helpful. Some species actively prey on corals.

Also, do you have any peppermint or harlequin shrimp? Both species have been known to attack LPS corals in the absence of their natural prey.

 

Sounds like you might have a hungry carnivorous starfish on your hands. Also, just a suggestion of course but it's possible that your acan got plucked due to food being on there polyp and a fish ripped it out. I feed my tank mates while I feed my corals because I've seen this happen.

 

Here is a picture of one of the acans and a picture of the starfihs. I do have a tiger shrimp but no others.
My thought as to why it is not the starfish is that I have had it for a good while and it has not bothered anythign.