So I'm like 99% sure this nerite snail died, it doesn't smell *horrible* but close to my nose it's fishy. But the fleshy part is hard as rock. He hasn't moved for 3 days. I kept finding him flipped upside down and he's HUGE so I think he's just old. But my question is, should I leave it in the tank? Weird, I know, but isn't the shell calcium, and would slowly release calcium for my other snails as it degrades?