My zoas are dying

[deepblueat2814]

My tank is predominantly zoas and lps. But recently, some of the larger colonies are starting to show signs of deteriation (a patch of polyps are not openning up). I have tried to take the colonies out of my tank and do a fresh water dip, but that seemed to be too late.
Today, my other colony about 7" fire and ice zoas is showing the same sign with some patches not openning up at all.
Can anyone tell me what are the possible cause and possible remedies before it's too late as I have a beautiful 5" metallic blue zoas that I don't want to have the same fate?

 

[Bebo77]

have you changed anything in your tank.. salt? new additions? lights?

 

[deepblueat2814]

I haven't changed anything at all. Same salt, same salinity, ph is at 8.23, calcium is at 420, zero amonia, 0 nitrtite, same lights for the past 2 years (although, I just change the bulbs about 3 months ago, but same brand and same kelvin rating). All fish and corals are doing fine for the time being (knock on wood).
I am at a lost

 

[LadyEquinox]

look very close for nuddies ,they look just like the zoa's they can even take on the color of thew zoas