Thank you for the response.
That's the part where I'm a bit confused, though. My water tests at a pH of 7.6, not at all acidic, and it's at least hard enough to leave scale on the glass whenever it evaporates. Could the water be lacking specifically in calcium, with other buffers affecting the hardness and pH, or is it more likely that I simply never noticed the state of their shells since buying them?
I want ahead and bought a cuttlebone today. Is there a chance that adding some to the tank will make the water too hard for either the nerites or the cherry shrimp in the tank.