I think my Pagoda Coral is dying....anyone with one, please help.

[disccollector]

I'm really hoping someone on this board can help me out. I purchased a fully stocked reef tank two months ago from someone that had had the tank for 8 years. The pagoda cup coral pictured below is the one in question.
The owner told me that he never feeds it anything and that good lighting was all it needed. So I've never fed this coral anything other than 12 hours of VHO (1-10k, 2 Super Actinics = 330W). However, it did have a 1 inch area on the right side where the skin had pulled away from the skeleton when I purchased it.
This didn't seem to be a problem because the polyps were generally all extended but for the past two weeks all but the polyps closest to the light have been closed and recessed. I've also noticed stringy stuff coming out of the recessed polyps every so often.
I've found so little on the Pagoda coral online...I have it at the top of my tank in moderate water flow on an angle. Maybe it should be completely flat? Should it be on the bottom? I have no idea. In reading most information on this board I'm beginning to realize that this coral probably needs to be fed something directly. What is the DT stuff I keep reading about? Where can I get it?
Everything else in the tank is fine from what I can tell. Here's my parameters:
sg 1.023
Ca 420
dkh 14
ph 7.7-8.0
temp 80-82
PO4 1ppm
Nitrate 15-20 ppm
Is there anything you can apply to the receding flesh to help prevent further erosion?

 

[disccollector]

bump

 

[peacetypes]

id say up the sg to 1.025or.024 and bump the ph but i wouldnt swear on it

 

[reef fool]

My pagoda did this on 2 occassions. Once, when it flipped upside down onto the sandbed, it didn't open for 2 weeks. I though it was a goner. Another time it flipped and was touching my torch coral. It even seemed to lose some color and show some bare skeleton in a few spots.Again, didn't open for a week or two.
It is doing great now, several months afterwards. No signs of any prior damage. It is now even beginning to attach it's base to the LR. I have mine at the top of the reef ( on a slight angle) w/ 800 watts of VHO.
Something is definitely stressing it out, making it slime and close up. If you find the reason for the stress, it should be OK.
Mine was actually a dyed coral when I purchased it (I bought it as a yellow pagoda) and it also survived that!
I would also try to bump up the PH and lower the Alk a bit.