Xenia disappearing

I have a few xenia colonies and about 2 months ago I fragged some onto a ceramic plug 2 small stalks.They were doing great pulsating ect.about a month ago the stalk on the left disapeared all that was left was a small pink spot where it had been so I thought my slug or something ran it over. well now a month later the small spot started sproting polyps so I thought cool.
now today the stalk that was next to it (about an inch tall) is gone with just a pink spot left? I got rid of the slug a few weeks back. I cannot figure out what is going on. the main xenia colony is fine even my small pom pom xenia are fine.:-/

 

Is there any other softies around it? My pompom was starting to show signs of distress and almost no pulse. I moved it to a better lit spot. Not sure if the frogspawn or the spaghetti leather may have done something to it. Hard to tell... but anyway maybe try moving it to another spot.

 

mine seem to like less light ... did you move these to areas with more light? whatever the answer, did you try the opposite? Mine seem really influenced by the lights.

 

no it was nothing like that they have been in that spot for a couple of months pretty close to the mother colony. Last night I went to bed a 3 am and when I looked today it was gone.
they were pulsing through the night. it looks like something ripped the whole stalk out and left a bump at the base.like I said the other bump has already started growing polyps back.so I don't know.
I'll get a pick of the plug there on.

 

Ok here is a pic I moved it to get a better picture. the one on the right has started with growing again the one on the left is the one that was gone this morning, it was about an inch high with about 15 big polyps on it.


also I don't know if this matters but last night when I checked my tank (with a flashlight..lol) there was a fuzzy chiton on the plug getting the algae.

 

I'd say NO3's PO4's and lack of carbonates and Ca. is the problem from the looks of the green on the bottom gravel and plug the coral was mounted to. ..

 

cal 500ppm
mag 1600 (raised in an attempt to fight algae problems) fighting a bad case of derebesia I think its called.
10 dkh
ph 8.2
no3s are 0 (due to the algea)
phos 0 (also due to algea)

I have allot of xenia in my tank and all the other colonies are thriving. also if that was the caes wouldn't they just disintegrate and not grow back?

 

That's what they look like after they are fragged. I thing something is cutting them and eating them. I thought Chitons only ate algae. Not sure if that is it.

 

xenia's can do some strange things.. I have a few in different places in my tank..
The other day, one of my big ones just fell over from the base..?
Still doing real good, but not going to stand back up.. So I think it's going to attach to the rock all along it's trunk and make a big colonie.. The rest of mine, no change..
But what happened to yours is strange..

Good Luck, Larry

 

Do you have a urchin in your tank, mine travels across my xenia from time to time like a bulldozer, pulling pieces off?