Hello all, I've had my tank for about three weeks and everything was going great. Then one day I look and all my snails were acting funny. (They were sitting upside down scrunched up.) Now their not even there anymore. They imploded. I had six, and now I have two. Weird thing is the ones that died were all my big ones and not the small ones. The little ones are still goin. The pet store guy told me he'd never heard of anything like that. Any idea of what it could be?