Losing Zoanthids\Haze forming over them?

[na1paj]

Assuming you haven't added anything new (especially zoas) that could carry pests, it's probably developing some sort of fungus. If it has a film over the closed polyps, if the polyps are turning dark or whitish in color, it's fungus.
it's not uncommon to have zoas develop fungus in the tank.
it's important to keep them in good water flow.

to treat it, what I do is take 2 containers about gallon size (3 if you think you may have nudis)

1st container - RO freshwater in tank temperature, add 1 package or 1 capful of Furan2/Bifuran, stir it up pretty well

2nd container - tank water and add iodine (read the directions for how much to add per gallon for a dip/bath, somewhere around 40 i believe)

for pests (nudis) - 3rd container - tank water with flatworm exit (read directions again)

place the zoa frag in the first container for 15 mins
then move it to the 2nd container for 15 mins (iodine helps recovery and tissue building)

if using 3rd container, another 15 mins.

return it to your tank under good flow

I've rescued many zoas this way. I also follow this routine when I get new zoas. good luck