I am new to this site, but after reading your post, I have had a VERY similar case, but the only difference was my gold had something growing from its side. About 6 months ago i noticed my fish had a large, about the size of a new eraser on a pencil, white mass growing from underneath the scales. While I was taking him out of the main tank to put him in the therapy tank the white thing fell off, leaving an open hole in his side. I treated the therapy tank with a bacteria treatment, parasite treatment and an antibiotic. fish got better.
when I fished out the white mass from the main tank it had a very specific metallic smell to it. odd if you ask me.
I am now in day 2 of treating my gold again, but this time he is spiraling, and had the large white thing come from his side in the same spot. Today it fell off leaving the same hole, just more red, I don't see the white thing this time. the only time he is not on swimming erratically is when he is resting on the bottom of the tank. the spiraling has been going on for quite awhile, but the scale loss and the growths are very recent. i hope the therapy works. i hope the infection hasn't damaged his ability to swim permanently.