Good info Slief. You must be an expert!
I've been in the hobby for about 27 years now and learned of lot of lessons over that time. Fortunately, I've only had a couple major issues during that time. While I am not bummed about not keeping hippo's the powder blues are one that I really like but because of their sensitivity to ich, I've avoided them since my last ich outbreak 4 years ago. When it happened, I had a really healthy and thriving reef with 40+ fish in my 500 gallon display. I did a major water change of about 100 gallons and forgot to check the water temps of my new water. More over, I forgot to heat it. The water change resulted in 4-5 degree temp drop over the course of about 30 minutes. A few days later the powder blue broke out in a bad case of ich. Within a day or two of that, one fish after the other broke out. Given the size of my display and the amount rock in it, capturing and QT'ing fish was not an option. My only option was to use reef safe ich remedies, lowered salinity (I couldn't go hypo because of my coral), increased water temp, garlic supplement, UV sterilization on very slow flow, increased O2 into the water, etc. Nothing helped. In the end, I lost 60-70% of my livestock which was heartbreaking. Especially because some of those fish were with me for several years and many of them were regular breeders.
The lessons I took away from it were as follows. First and foremost, be very cognizant of the water temps when you do a major water change.. It's well known that rapid temp changes are most often the root cause for ich outbreaks. Avoid certain tangs. While that isn't a concrete way in avoiding ich, certain tangs like hippos and powder blue and powder brown tangs seem to be more susceptible to breaking in ich. With those species, it doesn't take much. Even a little stress caused by an aggressive fish can trigger it.
Many here say that with proper QT'ing and a fallow tank, ich can be avoided 100%. I'm not a believer in that theory. In my opinion, even it that were possible, with corals coming into our tanks, live rock etc, eventually ich will be introduced into the water. That's not to say the fish will break out in it but it's presence is almost a certainty at some point regardless of it being visible. The key in my book to avoiding breakouts is avoiding temp changes, not introducing fish that are prone to breaking out and keeping stress levels down in the tank. The latter can only be done by not overstocking a tank, not keeping too large of a fish in a display that isn't appropriately sized and not introducing aggressive fish or at least removing any aggressive fish.
Like I said, I've been keeping salt water fish for 27 years now. In the last 20 or so years since I got my 500 gallon display, I've only had 1 ich outbreak and that one was completely avoidable. I never went fallow after that outbreak and I began restocking my fish within 4 weeks of the last signs of ich on the remaining fish. I was careful as to which fish were introduced first and made sure to avoid certain varieties. It's been four years since then. Now I have upwards of 70 fish in my display and I've never had a reoccurrence and I don't plan to either. But it kills me because I really love powder blues and it's terribly difficult for me not to tempt fate.
