I think it is more like algae or organic growth. It looks like a slimey film (corrosion will look more like mineral deposits that I don't see in your case). It's not corrosion.

Just use ketchup or a mix of vinegar and salt to clean them off, rinse them very thorougly. After refilling the loop with distilled water, just add 1-2 drops of biocide (like PT Nuke or anything containing copper sulfate) to kill algae.