Mini zoas from fiji

[Reef.ductionist]

I have noticed over the years from purchasing various zoos that one smaller species in particular-mini zoos usually orange or blue seem to just slowly shrink down and dissapear over a few months. However other very colorful species of zoos of medium width(1centimetre) or larger zoos I have aquired never suffer this fate.
Anyone experienced this firsthand also?
I have read articles 'suggesting' that bristle worms may feed on them but have never witnessed that.
Anyone know if these zoos are being collected from very deep reef waters? ...or if perhaps they are maybe more succeptable to higher nutrient systems with nitrates in the .1 ppm to .3ppm range?

Included are two images: IOne image is of medium and large colonies in my tank that seem (for all appearances) to be thriving. The other is a pic of the mini zoas that have not opened for five days.

 

[Reef.ductionist]

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