That’s why I went with a CFC vs. a plate chiller. Although I admit that recently I’ve been looking into plate chiller that can be broken down. This would really speed up knockout times, especially in the summer with increased water temps. Seems to be cost prohibitive though. Cheapest one I found was $850.00.
The darkness water you’re seeing is most likely corrosion. I wouldn’t soak SS and copper in PBW at the same time for long lengths of time as the 2 different metals can promote quicker corrosion.