Unexplained fish deaths - any ideas?

[kaz1961]

I have had three mysterious deaths in the past few weeks. The tank is a 150 high with a 30 gal display refugium and a 40 breeder sump. Parameters are sg .024, ammonia 0, nitrite 0, nitrate less than 5, calcium 380, phosphate less than .25, ph 8.0, Alk 10. About two weeks ago I had a Racoon that was in the tank for about two months die. About a week later a Flame Angel who I had for about a month died. This morning a Skunk Clown that I have had for at least 3 months was dead. All three fish were eating well and looked fine the night before they died then they were dead on the bottom the next morning. Current stock list:
4-5" Queen Angel
Coral Beauty
Falco Hawk
Flame Hawk
Spotted Hawk
Matted Filefish
2 PJ Cardinals
2 Ocellaris Clowns
CUC - CB shrimp, Fire Shrimp, Peppermint Shrimp, assorted snails, green crab, couple of small hermits. Refugium has about 5 different types of Macro algae, 1 Gorgonian, assorted Mushrooms, a small finger leather frag and a few one or two poply zoas.
I change filter socks every two days, 25 gallon water change every Saturday using I/O salt and R/O water, Reef Octopus skimmer running 24/7. Tank has been setup for almost a year and my maintenance schedule hasnt changed. My Wife is convinced that some foreign substance is poisoning the fish. I tend to think not because its only three fish and they died weeks apart. Wouldnt poison or soap residue etc kill the inverts before the fish? Any thoughts would be greatly appreciated. Thanks

 

[McPuff]

Are you QTing and treating the fish at all before adding to your display tank? It's possible they came in with something that festered and eventually killed the fish.

 

[Gone Tidepoolin]

+1 in the QT.
How big and aggressive are the hawkish?

 

[kaz1961]

No didnt QT the latest addition which was the Flame Angel. I did treat the tank that he and the Raccoon were in with Prazipro when I added him. Hawkfish are small, all three are each less than 2 inches and just lay around on the rock and never seem to bother anyone.

 

[Dmorty217]

Do any of these fish that died hang out in one spot or stop eating before hand?

 

[scooter31707]

Now that look at your tank size, you might want to keep an eye out on that Queen Angel. All the fish that die could have been a threat. IME, I have had some good and bad luck with angel and butterflies together. It definitely could have seen that dwarf angel as a threat. All in all, I agree with the others ^^^, quarantine is key and I would start looking at some possible parasite.