I'm not sure about the calcium thing, but my snails get that way when
they get old. None of my younger snails have it, but once they get, it
seems to be a sign of "old age". I usually have my snails for about two
years before they develop it. I'm not sure, but I think it might be
"molting" its shell al ittle bit but doesn't seem to fall off.

AD

Darren wrote:
i have maybe a dozen snails in my heavily planted fish tank, and all have
very thin shells with white encrusting spots on their shells. is this a
sign of a Ca deficiency? the local water supply reported the our water has
a range of 4-31ppm Ca; how is this level?

tai, darren