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?

4 is very low, 31 is typical of medium soft water. What is your GH? Do you see
signs of calcium deficiency in your plants? Look he
http://www.csd.net/~cgadd/aqua/art_plant_nutrient.htm

If you need to add calcium, there are many cheap sources. Ground up seashells,
Lime (calcium carbonate), and aragonite gravel from a sal****er tank are
popular. May fish stores sell aragonite by the pound, so you can buy just a bit
for $1.