I have a frag of zoanthids on a rock. The rock is on the sand bed against another rock. The ones in the middle of the colony are not opening. I was told that they are getting to crowded. I was wondering why they are not spreading on the rock. What can I do to help it. If they die off will see any spike?
Hello Pvillarraga, sorry to hear about your lack of polyp expansion. In my personal opinion I wouldn't dip them just yet. I just feel there is far too much dipping these days without some Q & A which could easily resolve your issue. When there is a polyp issue, the popular first response is to dip. Why? While proper dipping is safe, though stressful, it can exacerate and innocent situation. I would first ask...
1. How long have you had this frag?
2. If you just received it, was it picked up or shipped, recently fragged, how long was it allowed to heal before shipping/pick up?
3. If shipped, how, wet, dry?
4. If recently received, did you dip it then?
5. If so, how long ago was that?
6. If you performed a dip with do signs of nudis when you received it, and no sign of eggs, juvi or adult nudis via the dip or a visual inspection were found or seen, and you haven't added any new purchases in the last month, you don't have nudis.
7. What are your parameters?
8. Even though your other polyps are fully expanded, there can be other frags, polyps and even mother colonies which might not expand. This is why knowing what your parameters are across the board before making or taking any corrective actions if any at all.
9. If just received, did you light acclimate them?
10. Have you seen this link -
http://www.reefcentral.com/forums/showthread.php?t=1154238&highlight=why+your+polyps+won+t+expand
11. I am working on an update list that includes 5 additional reasons why your polyps might not be expanding. Here's 3 that are applicable to your situation.
(a.) Know your frag and your source - by that I mean, most of what is being sold are tiny 1 to 5 polyp frags or small chip frags as seen in your pic above.
Improper, Excessive or Prematurely fragged polyps can and will cause the very retraction you are seeing and even possible mortality. Dipping won't resolve your issue if that is the case.
There could very well be absolutely nothing wrong as most polyps are tempermental and just don't won't to open some days. I have own hundreds of colonies and have lost count of how many times I had some that didn't open for a few days. I knew my system well and knew there was absolutely nothing new, wrong, changed, updated etc. I waited a day or two and they would always reopen with absolutely no issues.
I would read this link at the top of the page,
http://www.reefcentral.com/forums/showthread.php?t=1852463 provide as much feedback as possible then read the first link and see if anything rings a bell. All of which can be done in 5 minutes, then you can dip if nothing rings a bell. I just feel if there is no discussion to solve an issue, nothing is gained if the situation presents itself again. Just my opinion and no offense to anyone else. Good luck my friend, I hope something in all the replies helps and I would worry just yet.
BTW, I see no signs of infection, fungus, pinching, polyp degredation, bleaching, expulsion etc. I see a slight hint of color through a few polyps which means they aren't even tightly cupped. They still appear full bodied/fully formed with no flaking even while retracted. All good signs.:thumbsup: so yes, they can be saved.
Just to put you at ease, here's a reefer just below your post who had retraction for several weeks. His polyps reopened on their own.
http://www.reefcentral.com/forums/showthread.php?t=2190131
MUCHO REEF
TOTM - August 2003
Do you have any photos you could share with us, maybe we can get to the bottom of this! 
