Ramshorn Snail with cracked shell

I recently removed a new Ramshorn snail from quarantine and noticed
it's shell is cracked. The snail is small, smaller than a quarter, and
the crack goes all the way across his shell, about 1/2 back from his
opening. Unfortunately it looks like a pretty deep crack...I'm not
sure if I got him that way and didn't notice until now or he injured
himself somehow. I have Googled and could not find any relevant
information. Does anyone know if this will affect his health? He is
eating, motoring around and otherwise being a normal snail.

Also, in searching around I found a site that said snails should
receive calcium supplements. Does anyone know if this is necessary for
health and how I would provide this?

As always, any help is greatly appreciated!