I was about to say Jed58, $6100 is a steal on ESS-13! My quote i'm thinking was closer to 12-14k range!! That stuff has small particles of Gold and Platinum dust in it that help seal off the bottom ..that has to be it! If you can get that pond sealed for only a thousand dollars I would be very happy! It's a great pond! I think we all wished we'd known more about pond building before hand but hey that's what makes life interesting...you learn as you go. I would definately recommend adding bentonite with it if you have the extra money. Any organic matter or material the DB-100 has to attach to...all the better for the sealing capabilites.