Yea I learned this way too

Lost almost all of my stock and I finally decided to get a QT... SOMEHOW?!?!! Still got ich in my tank right now... My fish seem to be healthy enough how ever to fight it off and I honestly have NO idea how it got back in my tank I took every precaution and still.... ugh
Anyways, I ran my tank without fish for 12 weeks.
I had fish in quarantine after the 12 week period, and treated them in a 20 gallon quarantine tank bare bottom nothing in it but PVC tubing, and a filter with only filter floss.
I treat all of my new fish with copper, specifically seachem Cupramine for 18 days in quarantine.
I mean I THOUGHT I was doing it right? I haven't lost any fish but every once in a while I do see my clown and tang with the occasional break out of 1-5 white spots... then I see nothing again for a while... Like I said I haven't lost anyone, but my fish DO flash so I know something is irritating them whether those white spots are ich or not.
They haven't stopped eating or anything...
Considering going 12 weeks again with all of my fish in quarantine and my display empty...
Really p***** I can't seem to get rid of this bloody parasite.