As a proponent of natural filtration producing in tank live food to promote healthy immune systems in both fish & coral. I have not quarantined in 35 years of 47 years in keeping marine tanks. I have seen ich twice in my systems. The first time I saw ich was on an established mature 10 year old system that had not seen any additions in 2 years. Following a loss of power stress event, I saw Ich everywhere in 1000G extended system. I reestablished stability and ich disappeared. Ten years later, I saw ich thru shipping bags on seven tiny Hippo tangs. Fish were sideways and showed great stress in color loss & eratic breathing. I made an executive decision and immediately released tangs into fife teen year old tank that had ich five years earlier. Scratching & itching behavior was evident on all new tangs, four showed obvious ich spots in the shipping bag after a 90 day quarantine at DD. After 3 days, all ich spots disappeared. After 7 days all scratching & itching ceased. That was ten years ago. Do I have dormat ich in my 25 year old tank? Probably. After I went through the first ich episode 25 years ago, I started reading scientific papers on ich with the wisdom at the time for fallow period was 14 days. The days to fallow have increased from 14 to present 76 day fallow period. The fallow period has been increased because it is not absolute. I continued reading research paper in detail and one phrase stuck out, “most cyst will hatch in X days”. Nature will survive.