I feel your pain, I am sure that MOST people here feel your pain. The sad truth is that QT and treatment is a requirement of the hobby.
Lots of people don't like to talk about it but the industry has a dark side... a dark side littered with dead fish, cyanide killed reefs, etc. So for me, if a fish gets plucked from a reef, thrown in bags and flown half way around the world to a pet store, I am going to do EVERYTHING in my power to keep him alive. Lots of fish die because people simply don't want to QT them and it really is not hard nor expensive.
Here is the other part of the equation... THERE IS NO HALFWAY!! QT everything wet or don't bother. When you get complacent.. then is when it will get you.
I have a 300 gallon with LOTS of fish and lots of big expensive adult tangs. I QTd them all and things were great. I decided I really liked acans, and bought a pack of five of them. I didn't have my coral QT up and running at the time so I threw them in my frag system that is connected to my DT. One week later...hippo had ich, then the fox face had it, then my Achilles had it..
Soooo.. I had to set up 200 gallons of temporary tanks, pull all the fish out of the DT (you want pain?.. try getting 9 anthias out of an sps tank). I had to tear all the rock work apart.
It was depressing and I just left my rock in the fuge for like 2 weeks. BUT, you have to make lemonade.
I re aquascape the entire tank.
I glued up and sold most of the sps frags I made while breaking them.
I cleaned the entire system.. I don't think it was this clean when I bought it lol.
And now I am adding pods so they can explode without my wrasse eating them.
A coral QT can be as simple as a couple t5 lights over a 20 gallon with a powerhead and a heater.
lastly, never add prime to a tank with copper in it!!
Step back, re group, and come back, you got this and it will be rewarding!
best of luck