I feel you. I had an Ich outbreak with 11 fish, and had to do something similar.
The key to avoid frustration is to deal with these as separate challenges and not look back on what has already been resolved, IMO. No sense in carrying that extra baggage around. You've dealt with the Bayer incident, so close the book on that one. You're done with QT for now, PBT is history, so close the book on that, too.
So, the next challenge is GHA. At this time, that's the ONLY challenge, right? And what self respecting reefer has not faced a GHA challenge

. Clear the history, and work on GHA. The usual basic stuff is a good start. Less light or a period of no light, less feeding, more frequent DT water changes, 0 TDS RODI, etc., etc. Sea urchins, snails and other algae eating CUC are another option. You can keep your QT going and pick another herbivore, like a dwarf angel or tang, to eat the GHA. Keep your chin up and all that jazz. These are the usual challenges to reef keeping, and they can be fixed! Been there, done that!