So, what's the explanation here?

[Goldfish loach boy]

This is a but weird, well for me at least here is the story
I've had a total of 4 mystery snails in my 55 gallon tank, when they all reach a certain size, they die, like all of them died at the same size
Like a month or more ago, I bought two gold ones, one for my 5 gallon and the other one for the 55, well yesterday I added the one from the 55 to the 5 gallon and I noticed something, the one from the 5 gallon is a lot bigger, like double the size of the one from the 55 gallon, and looks a lot healthier. Even though they were the same size when I got them, what's up with that?
Thanks!http://i1281.photobucket.com/albums...0BF898B-6297-000008DBCFDEC3BB_zps90714e95.jpg http://i1281.photobucket.com/albums...AF1A5E0-6297-000008DC0C074C3A_zpsc6c02132.jpg
http://i1281.photobucket.com/albums...sc3b661f7.jpg000008DC30949DB7_zpsb33d83d7.jpg

 

[hijnx]

Are both of the snails in the first picture? I spy with my little eye, a nerite snail.

 

[Goldfish loach boy]

Oh yea there is also a nerite in there ill get a pic of both