Peeling Pagoda Cup Looking for advice

[jessejen2013]

We have had a beautiful pagoda for nearly three months (first coral in the tank set up at Christmas time). It was absolutely thriving even before increasing the flow in the tank over the past few weeks. Just over a week ago we added a RBTA and rearranged the tank to show it off. Since around that time, maybe a couple days before the pagoda's tentacles have not been fully extended like normal. Today we noticed a fairly dramatic peeling toward one of the edges (one with least amount of flow). The only recent changes have been moving LR around in the tank, trying to be mindful of not altering the flow to the pagoda. About this time I also have been cutting back on feeding due to a spike in Nitrate/Phosphates. I had also been running a cheaper carbon in my filter, which I have recently changed to matrix.

Water Parameters:
Salinity: 1.025(by refractometer)
PH: 7.9
Ammonia: 0
Nitrite: 0
Nitrate: 10
Phosphate: 0.25
KH: 10
Calcium: 520

I will attach a picture of how it looks now vs how it looked 2 weeks ago.

Tank: 32 gallon Biocube LED with InTank insert (filter floss, matrix, purigen, phosguard, & Chemi-Pure blue) and Tunze 9001 skimmer. Cobalt MJ 1200 for filter with Hydor rotating deflector and Hydor 425 powerhead for flow. 20% WC now twice a week due to amount of livestock.

Livestock:
31 lbs LR & Sand
Purple Fire Fish
YWG
Royal Gramma
Hector Goby
3 Ocellaris Clowns
3 red legged hermits
fire shrimp
banded pistol shrimp
blue tuxido urchin
20+ snails
sand sifting starfish (no comments please)
RBTA

2 Duncans
Frogspawn
3 Mushrooms
Red Lobophyllia Brain
Blue Sympodium
Trumpet
Superman
Large Polyp Blasto
Small Polyp Blasto
Favite
Daisy Polyp
Pagoda Cup Coral
Zoanthids