Hello all. Received this sun coral as a gift a few months ago and it has been doing well up until about a week ago. It would open daily and we did target feed it when it fully opened. About a week ago it stopped opening and is now beginning to look pretty bad. Water parameters: Ammonia: 0 Nitrite 0 Nitrate 15ppm - see note Calcium 440 Alk 8.4 Ph 7.8 Mg 1280 Temp 78 - 80 depending on time of day and ambient temperature. Am pretty new to this hobby - (we have had issues with nitrates running between 15 and 20ppm despite weekly water changes - recently upgraded protein skimmer to try and work on that.) The system is a 90 gallon we purchased at 3 years old - it has been stable - the nitrate level coming down very slowly with some diligence in water changes and the addition of a refugium about a month or so after getting the system (it was fish only on purchase. ) Lighting Marineland Reef Capable (not impressed with these but invested too much to replace them now but considering replacing the T5s that came with the tank. ) Other corals are doing well (torch, trumpet, ricordia, mushrooms) with the exception of another gift - an astromellussa. We did lose a war coral frag early on but others have all done well. I am beginning to wonder if the flame angel has been nipping at their tentacles. I see it do that sometimes. Though water parameters aren't perfect (nitrates still between 10 and 20) this coral did well for months under those conditions. The only other change is the addition of two mandarins - both of whom are eating well off the liverock (we waited until we had a good copopod population both in the fuge and display before getting the fish.) Any help or advice welcome.