We recently switched from a galvanized water supply line (that failed) to pex, and added some new copper supply lines. We're getting a blue-green deposit in the tub where the spout drips while we are showering. This never happened in the 20 or so years prior to the changes described above. I'm worried about corrosion inside the copper pipe, possibly from electrolysis or from wrong flux. Anyone know what's up with this?