Get the H2S out
Did a copper fining bench trial on the zin. I tried 0.0, 0.3, 0.6, 0.9 ppm trials.
The difference between the untreated and the 0.3 was clear. Lots more fruit on the nose. Clean and crisp. The 0.6 was almost the same as the 0.3, except less fruit. I have heard that the cu can strip flavored in addition to the H2S.
In the end I decided to go with 0.3 ppm. I will wait for the MLF to complete, then sulfite and copper at the same time, with racking a couple of days later.
Try an aerative racking. Use copper as a last resort. If you do go with the copper try smallest amount. Allow a couple of days and re-dose if necessary.
Best O Luck.
Thanks for the comment. I have aerated this one several times, which has helped, but still have the problem.