Part of my Xenia seems to be dying. Other corals are doing apparently great (Elegance, Euphilia, Blastomussa, Zoas). I can only think of two things: it's a bit off the middle may be getting too strong light (RSX150 Maxspect LPS Auto setting) or the phosphates which for some reasons are 0 even 24 hours after dosing NaH2PO4. The tank is high in nitrates (40ppm).