I've had my 75 gallon tank up and running for about a year. I had two blue oranda's, an orange ryukin, a red and white ryukin, and a little green ranchu. Never had a problem, everything going well. At least a 50% water change per week, over 1000 gph in filtration. No detectable water quality issues or anything I can pinpoint. My big orange ryukin finally died due to persistent floaty issues, so I bought his replacement a couple of weeks ago. I should have quarantined, but I didn't. About a week ago I started to see some cloudiness on all of the fish. A few grains of salt on some fins. I started the salt and heat treatment.The ich multiplied and covered most of the fish, but they still were eating fine. Respiration was normal. Then the fin rot started, shredding all of those fancy tails into ragged strips. The ich only got worse, overwhelming the eyes and the respiration became rapid. No interest in food. What was left of the tails became streaked in red, followed by red blotches on the bodies. Lost all five of them in less than a week. I've kept salt and fresh aquariums for years, and I've dealt with ich before. But this...it was like I never had a chance. My question....what was that?