Originally Posted by brewingbarrister
The reason I ask is that I let mine soak in water and bleach solution
Why are you doing that? I wouldn't use bleach on copper. Don't use it on stainless steel either BTW.
That green stuff is copper salts (copper chloride, copper sulfate) from corrosion accelerated by the bleach solution. If it's only a few small spots it is probably not enough to worry about. A small amount of copper will dissolve in the hot wort even from a clean chiller.
For future reference, after use rinse the chiller with clean, hot water. If any crud is sticking wipe it with a sponge or scrubby if necessary along with a good brewery cleaner like PBW. Rinse it again and put it away. To make it shiny before using rub it down with an acidic solution like Star San or distilled vinegar. Rinse and drop it in the brew kettle. An immersion chiller just needs to be clean before use, not sanitized. Five or ten minutes in the kettle before flameout will take care of that.