Snail shell cracking

[smsturner]

I have had my mystery snail for well over 2 months and we love him. He is fun to watch and is playful. He likes to sit over the bubble strip until his shell fills with air and then he "flies" to another part of the tank.
He has been growing since we got him and now he seems to be getting these big cracks (2 fo them) along the top of his shell. Is there something we can give him (certain kind of food?) that will help? What causes this?
-Suzy

 

[drobbins27]

What else is in the tank? Any loaches?

 

[smsturner]

No, none of my fish are interested in eating him!
I have swordtails, 4 swordtail fry, and some guppies in with him.

 

[Pugwinkle]

Is your water hard or soft? You could put in some cuttle bone if your water is soft.