Thank you for detailed information!! Yea, I really didn't want to dig, but you're talking me in to it.
I seen this pond here,
Spring time Pond (Pic) Can't wait for good weather. and thought it was really nice, I would want something on a smaller scale, but I'm wondering with the dirt/sand in between the brick work and pool liner if that would lend some insulation. Also, I didn't mention that this would be in a mostly shaded area of my yard and I have about a 10x12 area to work with.