More than likely, you are looking at oxides that are dissolving in the carbonated water. I'd flush the system with a scale remover like Beer Line Cleaner.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk