I have some apple snails and I'm a bit worried about their shells. I want them to be as strong as possible, and right now I don't think they are. (Although, they don't look that bad at all, I just think they could look a little bit better.)

I have heard of adding eggshells to the water, could somebody give me specifics? (How many eggshells, do I put them in a mesh bag in the filter or what, will this affect my water parameters or other fish, etc.)

Or, should I use the liquid marine calcium, and if so, how much should I put in?

I do have pretty hard water, 7.8 ph, and they get a varied diet of fish foods, algae wafers, bottom feeder wafers, crab cuisine pellets, and zucchini. And tank algae, of course. They seem healthy, I just want good strong-looking shells. 

Thanks!

x-posted tomystery_snails