Hi I'm new to fish tank keeping and I really like the snails but I have been having problems with some of them. I got some giant ramhorns and nerite snails but they all started to retract into their shells. They would retract really far so you could see a lot of the inside of their shell and then would die. Now it is happening to my adult mystery snail that I've had for almost 4 months. I'm pretty attacted to it and would really like to know what is happening and if I could do some thing to fix this problem?