I have a 125 gal FOWLR marine aquarium that has been set up for abut 18 months. It has an attached 40 gal. refugium with 3" sandbed and calerpa. pH 8.1-8.2, S.G 1.021, zero nitrites and ammonia, 10 ppm nitrates, 30% water change per month (Instant Ocean), temp. 78-79F. 5 80 watt T-5 lights. 2 36 watt UV sterlizers. Water circulation about 14-15 gpm. One 5" queen angel (until recently), 5" blue face angel, 5" emperor angel, 5" purple tang, one 5" blue hippo tang, 3" keyhole angel, 3" yellow tail poma angel, pixie hawkfish, flame hawkfish, longnose hawkfish, 2/1/2" royal gramma.
The queen angel was added about 14 months ago. It did fine from the beginning. A couple of weeks ago, I noticed that it's breathing rate was about twice normal and it stopped eating. It was always a very agressive eater. It also appeared to be trying to spit out something. No visual evidence of parasites, bacteria, or injury. Thinking the high breathing rate might be caused by gill parasites, I did a fresh water dip. It didn't help. It died within 3 days from the time I discovered these symptoms. It's possible it had the symptoms longer than that, but not much longer since I look at each fish twice a day during feeding. About 10-12 hours before it died, it developed some red "veins" in it's fins like it was hemoraging. Other than that, the fish looked "good", even after it was dead. Since I think it's extremely unlikely that a healthy fish will get a parasite or bacteria attack and die within a couple of days, particularly when there's no visual evidence of such, I'm puzzeled by what caused the death. All the other fish are doing fine. Any ideas?