whats causing these to die?

[rnyce]

Hi Guys,
not sure what these corals are called. but i had hundreds of them on the rock and on the side of the tank. And slowely over the last 6 months they are closing and dying one by one. Almost like something is eating them or im not sure what it is?
I have dipped them but doesnt seem to help?
any thoughts
http://i378.photobucket.com/albums/oo224/rnyce/IMAG0790.jpg

 

[Owen386]

Button polyps.

Depends on alotta of factors. Tank parameter? How's long you been up and running? What are the other tank: inhabitants?

 

[dz6t]

lack of water flow can cause rot for these polyps.

 

[JayM]

so can zoa eating nudis, but in general they are very, very hardy

 

[jt628]

There has to be some sort of underlying issue, I put at least a colony a month in my sump to kill them off, they spread like weeds generally...