It really sounds like you want a pool, not a pond. Maybe think about approaching it like a garden pond. I know that they sell filter systems and such for recycling the water. I don't know if it would work on that big of a pond. I think a liner would work best for you. I agree with esshup's warning about using pool chemicals in a pond. Good luck with the project and keep us posted.

Brian
Retired Coach

Just another day in paradise!