Zoa's receding?

What would be some factors that cause a colony to recede or seem to just dissappear? Over 2 weeks in the tank the colors are coming back, the center heads are looking bigger than ever but the ones on the edge seem to be shrinking and going away? A second colony added the same day and same placement has not increased in color but seems to be spreading from the frag rock? Any thoughts before I randomly start moving things around?

 

Take a flashlight to your tank late at night.
If they are being predated then the two most common culprits are sundial snails or zoa eating nudibranches. The good thing is, sundials are pretty easy to spot. Irritate the polyps till they close and probe through them looking for something like this:


or this:


Otherwise, what do your water params look like?

 

To be quite honest it looks like the individual polyps are just decreasing in size daily and slowly receding. My water params are good except phospahte (2-5ppm down from over 10?) which I am really trying to bring down. I dont test for cal/mag yet but I intend to soon. I only have a few anthelia colonies and didnt see the need to test those asap. I have read that zoas were fairly hearty and a good beginner coral and this is the issue i am concerned with.

as of last friday i usually test weekly...
nh3/nh4 0
no2 <0.3
ph 8.0
kh 7
po4 2-5ppm range <testing daily for 2 weeks seems to have leveled
s.g. 1.023
temp 79

I am getting a phosphate reactor today and probably a good cal/mag test kit.
I also read they feed by photosyn now I am reading they need to be fed???
my lighting is 2 pc's for a total of 4 65watt 10k's and 4 65watt actinics on a 140gal,wet dry,sump,octo150

 

Zoas are usually good sans food, but they will feed on particulate matter in the water column. How much lighting are you running on the tank? If they are receding and disappearing I would highly suggest doing a parasite check tonight

 

Sorry I just updated my reply

 

Did you dip/quarantine the zoas at all before introduction?

 

No I didnt, I wasnt aware of the dip at the time of purchase I just read a little on it. Here in Florida I struggle to keep my tank cool as it is and although i know a q.t. is reccomended I am still working on that as I am still learning every day.

If something was eating them wouldn't both colonies be affected? They only sit like 6 inches apart on separate rocks in the sand.

 

Possible, but not necessarily. Sundial snails can do a tremendous amount of damage in a short period of time. Might just be on one colony at the current time.

 

Ok its 1:30 a.m. and I just inspected the tank and realized I need new batteries for the flashlight now too. Good thing for the led fishing headlight!! I promptly found an emrald crab posted up next to them. (the ones that are receding....) He seemed at first to be grooming around the closed heads as a crab usually does probing around the heads. So I scoped around elsewhere and really found nothing unusual except these bizarre tiny red spiraly swimming worm things(very small and fast). Nothing evident elsewhere on the colonies or anywhere else for that matter. So I looked over the receding colony one last time and that crab was pulling away the base of the growth edge and eating it. So he went in the sump.....I was kinda freaking because I never thought he would be able to catch him and he would just slip away in the rocks. But his polyp eating days ar numbered nonetheless. I did get a reactor today and plan on getting the phosban bag out of the sump and in the reactor today at some point.

 

Excellent! Not the polyp eating crab, but that you were able to identify and catch him. Usually it is just a matter of keeping your eyes open and being observant.
Now if I could just catch the little bastard(bastards?) that are making a meal of my ultra-blue zoa's