soft coral dieing need help

Pulsing xenia? I've never had them, but I've read they are really sensitive to any kind of change in water chemistry.
Sounds like everything you are doing is right...perhaps in too high a flow area? Or not enough flow?

Are they deteriorating/falling apart or just closed up? Perhap new location is not as favorable as previous location in reference to water movement??

When dosing Phyto, are you doing right on top of by the return spout?

I am guessing pic above is before moving?? If so, any new pics?

fsn77 is right about feeding. Xenia doesn't feed in this regard and for all intents and purposes, don't even have a gut (it's there, but highly reduced). They are largely absorptive feeders, relying on that and photosynthesis for their needs. That being said, you are likely experiencing a typical Xenia "meltdown" reaction. It may be related to exhausting some particular nutrient in the tank (as tanks with higher levels of nutrients tend to do better with it), but it is not known exactly why it happens.

It's been my experience that xenia may be unhappy for a bit but they are hard to actually kill. I've accidently left mine in an unheated container with no movement when I was moving my tank and didnt see it at the end, found it all jelly (didnt have any stalks or anything) and stunk terrible. A friend of mine on another forum told me it might be ok so I put it in the tank and 24 hours later it looked alot better and within a week it wes better than ever. They don't like to be messed with and take a bit to get used to a new location. they require a fair amount of light and some nitrates. after 2.5 months mine is now over 8" tall. I have mine in alot more flow than most I see, but that doesnt seem to matter. So i'm gonna say its either not getting enough nutrients (light or nitrates) and or its getting moved messed with by something often. maybe a clownfish likes to mess around in it or an active fish often swims by its location and brushes it as it goes by.

Get your dkH to 8-10.

How often do you feed the fish and how frequent are your water changes? In my 20g I have done 2 or 3 water changes in 6 months and feed twice weekly. The xenia does well. In my 60 I feed sparingly and change 10g weekly. Xenia does not last long in that tank. I know they won't actaully eat food like LPS, but from my and others anecdotal experience, I think they need a tank that's a little dirty.