The issue I had with Zinc turned out to be in the Reef Crystals salt itself I mixed some salt with RO/DI and sent the sample for ICP testing and here was the results -
Someone wants to show you the water test results and shared this link to the evaluation. Click on the image above to explore the water test results.
www.triton-lab.de
I contacted Reef Cystals and gave them the results but they showed no interest in the problem. I therefore put the remainder in the trash and switched brands and will never use their salt again. As you will see from ICP test, there was some copper in the newly mixed salt as well.
Hope that helps.