ID Please? Green Star Ployps under attack

[Sonam]

Greetings,

We have a 125 gallon primarily softie system that is 3 years old.

A few days ago we found a gigantic nudibranch eating our green star polyps. We removed it and looked for any others. It must have matured in our system. We had added a coral several weeks ago that appeared healthy but then died. Some small white wormlike things were on it. We removed the coral and all the worms we could find.

Yesterday a zoanthids colony lost probably 25% of its polyps so I dipped it. There were tiny wormlike things but too small to make out.
Today our green star polyps are retracted and
I found this

the green star polyps are encrusting a large (too big to remove) rock. So I can’t dip it.
What should I do?

 

[TriggerFinger]

It looks like a mini brittle star leg. It might be irritating the zoa a bit but isn’t eating it

 

[Sonam]

Thanks.
Something is taking out our green star polyps. Doing a major water change today. Don’t know what else to do. It’s so sad. We grew these out from small frags.