Kohler Shower Heads Cleaning Green Buildup On Shower Heads...?

Cleaning green buildup on shower heads...? - kohler shower heads

How do I clean the collection of green and white Kohler pretty bad in my shower? I do not think anyone (including the previous owner cleaned), so it was probably the case for good 10 years. Are they worthless, or is there a magic solution to the Home Depot? What exactly - the hard water deposits or calcium deposits?

Thank you!