You will need to supplement them with sinking foods. Sulawesi snails get large and cannot live from algae and aufwuchs alone. Sinking algae wafers are great for them. Zucchini is a great treat for them.
One of the big things you need to worry about with snails is the water hardness and pH. In soft, acidic water their shells will dissolve away.
If they are in a planted tank, I feel I should warn you that some Sulawesi snails are known plant eaters.