I have what I believe to be calcium building up in my shower drain. Is there a chemical or mechanical treatment for this condition ? Please specify.

More likely human skin flakes and body oil than calcium. You shower head would clog long before you would see calcium in a drain. Mix 1/2 cup table salt with equal amount of baking soda and dump into the drain. Now add cup of white vinegar and watch the action, allow to sit overnight. Tomorrow dump a full bucket of very hot water down the drain, how is it looking?