I have exactly thirty ramshorn snails in a snails-only tank. Most are somewhere around three months old, so they're not all that big right now. I do have one larger ramshorn from a different tank, but all the others are the same age and mostly the same size. They were perfectly fine until I did my weekly water change yesterday, in which I cleaned all the gravel and the sides and the fake plant while the snails were in a small container. I put a small piece of food in there, which I usually don't do, but I did yesterday because I made some snail biscuits with a variety of mushed fish food, a quarter of a calcium pill (because it had vitamin D in it), and some crushed egg shells. They swarmed all over the food, and then I put them back into their tank, and they were all happy and went straight for the nearest leaf to grab on to. Then, in late afternoon-ish, I went to check on them, and every single one was lying on the gravel and not moving. They were all also pooping excessively (they've never done that before). I really couldn't do anything while they were like that, so I left them and this morning, they had stopped pooping, but some are completely inside of their shells. I checked the ones that were all the way retracted to see if they'd died. They haven't, or at least I can't smell the telltale stink yet. Some are out of their shells and move if I tap their shell, but none are crawling around like they usually do. I'm really worried about them, since I'm still at the point where they haven't become pests in my eyes. 
Did the vitamin D do something bad? Should I change the water (again) to get rid of all the extra poop? Or should I just wait and see if they make it?(I'm not too hopeful about that, though.) 
Or did I miss something? Thanks!
Did the vitamin D do something bad? Should I change the water (again) to get rid of all the extra poop? Or should I just wait and see if they make it?(I'm not too hopeful about that, though.) Or did I miss something? Thanks!
