If you have very soft water, then it would definitely be beneficial to add some calcium to your tank. The cheapest and haha, laziest way is to add some cuttlebone (you can find it in the bird section of a pet store). Just break off a piece and let it sit in a corner. I don't know if this is the most effective way though.
Other ways to add the needed nutrients for snail shells are to add crushed coral (bumping up your water hardness), or to add montmorillonite clay powder. You can get montmorillonite as a pond additive for koi.
Pond Fish & Koi Health & Nutrition: Microbe-Lift CMC Calcium Montmorillonite Mineral Clay
One 2lb jar should last you for the rest of your life because all you need to do is add a pinch's worth per gallon at every water change.