Hello, just bought 2 mystery snails today, 1 blue and 1 ivory, the ivory snail is still held up in it's shell since I brought it home about 2 hours ago at the bottom of the tank, the blue however has moved to the top of the water line. He's not trying to get out, it seems he's just sitting up top with his head poking out, is this normal? Thanks. I have a 55 gallon tropical tank, 77 degrees.