My nerite's shell developed a crack several years after I got it, but seeing how it doesn't seem to have bothered the snail yours should be OK.
Where is the break - do you mean the tip being broken off? All my nerites are like that, though mine are more eroded while yours looks like it's been sliced off with a knife!
How hard is your water? If it's middling to hard there should be enough calcium in the water without adding extra. If it's very soft you could try putting a small piece of coral or limestone in the tank - not much as you don't want to change the hardness or pH by very much.
My tap water GH is 5 dH, and I don't add anything. And I've had my zebra nerite for 9 years.
I have heard about people using tums but I'd rather not risk any other additives which is why I suggest a small piece of coral or limestone. The snail can graze on it without it dissolving in the water.