Looks like a Apple Snail to me, however, since there's more then one type, cana, brigg etc, I'd think comparing the charts on the apple snail site would be good for you!
don't just look at the color, the tell tales are in the spiral & operculums as to which is what!

Oh yeah, get a food clip that has a suction cup and just clip it inside the tank, they will find it!